Full oncogenic activities of v-Src are mediated by multiple signaling pathways. Ras as an essential mediator for cell survival

Oncogenic STAT Transcription Factors as Targets for Cancer Therapy: Innovative Strategies and Clinical Translation

Despite advances in our understanding of molecular aspects of oncogenesis, cancer remains a leading cause of death. The malignant behavior of a cancer cell is driven by the inappropriate activation of transcription factors. In particular, signal transducers and activators of transcription (STATs), which regulate many critical cellular processes such as proliferation, apoptosis, and differentiation, are frequently activated inappropriately in a wide spectrum of human cancers. Multiple signaling pathways converge on the STATs, highlighting their importance in the development and progression of oncogenic diseases. STAT3 and STAT5 are two members of the STAT protein family that are the most frequently activated in cancers and can drive cancer pathogenesis directly. The development of inhibitors targeting STAT3 and STAT5 has been the subject of intense investigations in the last decade, although effective treatment options remain limited. In this review, we investigate the specific roles of STAT3 and STAT5 in normal physiology and cancer biology, discuss the opportunities and challenges in pharmacologically targeting STAT proteins and their upstream activators, and offer insights into novel therapeutic strategies to identify STAT inhibitors as cancer therapeutics.

Natural bioactive compounds and STAT3 against hepatocellular carcinoma: An update

Hepatocellular carcinoma (HCC) is a challenging and very fatal liver cancer. The signal transducer and activator of transcription 3 (STAT3) pathway is a crucial regulator of tumor development and are ubiquitously active in HCC. Therefore, targeting STAT3 has emerged as a promising approach for preventing and treating HCC. Various natural bioactive compounds (NBCs) have been proven to target STAT3 and have the potential to prevent and treat HCC as STAT3 inhibitors. Numerous kinds of STAT3 inhibitors have been identified, including small molecule inhibitors, peptide inhibitors, and oligonucleotide inhibitors. Due to the undesirable side effects of the conventional therapeutic drugs against HCC, the focus is shifted to NBCs derived from plants and other natural sources. NBCs can be broadly classified into the categories of terpenes, alkaloids, carotenoids, and phenols. Most of the compounds belong to the family of terpenes, which prevent tumorigenesis by inhibiting STAT3 nuclear translocation. Further, through STAT3 inhibition, terpenes downregulate matrix metalloprotease 2 (MMP2), matrix metalloprotease 9 (MMP9) and vascular endothelial growth factor (VEGF), modulating metastasis. Terpenes also suppress the anti-apoptotic proteins and cell cycle markers. This review provides comprehensive information related to STAT3 abrogation by NBCs in HCC with in vitro and in vivo evidences.

The complementary roles of STAT3 and STAT1 in cancer biology: insights into tumor pathogenesis and therapeutic strategies

STATs are a family of transcription factors that regulate many critical cellular processes such as proliferation, apoptosis, and differentiation. Dysregulation of STATs is frequently observed in tumors and can directly drive cancer pathogenesis. STAT1 and STAT3 are generally viewed as mediating opposite roles in cancer development, with STAT1 suppressing tumorigenesis and STAT3 promoting oncogenesis. In this review, we investigate the specific roles of STAT1 and STAT3 in normal physiology and cancer biology, explore their interactions with each other, and offer insights into therapeutic strategies through modulating their transcriptional activity.

Functional roles of SRC signaling in pancreatic cancer: Recent insights provide novel therapeutic opportunities

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignant disease with a 5-year survival rate of <10%. Aberrant activation or elevated expression of the tyrosine kinase c-SRC (SRC) is frequently observed in PDAC and is associated with a poor prognosis. Preclinical studies have revealed a multifaceted role for SRC activation in PDAC, including promoting chronic inflammation, tumor cell proliferation and survival, cancer cell stemness, desmoplasia, hypoxia, angiogenesis, invasion, metastasis, and drug resistance. Strategies to inhibit SRC signaling include suppressing its catalytic activity, inhibiting protein stability, or by interfering with signaling components of the SRC signaling pathway including suppressing protein interactions of SRC. In this review, we discuss the molecular and immunological mechanisms by which aberrant SRC activity promotes PDAC tumorigenesis. We also provide a comprehensive update of SRC inhibitors in the clinic, and discuss the clinical challenges associated with targeting SRC in pancreatic cancer.

The role of STAT3 in leading the crosstalk between human cancers and the immune system

The development and progression of human cancers are continuously and dynamically regulated by intrinsic and extrinsic factors. As a converging point of multiple oncogenic pathways, signal transducer and activator of transcription 3 (STAT3) is constitutively activated both in tumor cells and tumor-infiltrated immune cells. Activated STAT3 persistently triggers tumor progression through direct regulation of oncogenic gene expression. Apart from its oncogenic role in regulating gene expression in tumor cells, STAT3 also paves the way for human cancer growth through immunosuppression. Activated STAT3 in immune cells results in inhibition of immune mediators and promotion of immunosuppressive factors. Therefore, STAT3 modulates the interaction between tumor cells and host immunity. Accumulating evidence suggests that targeting STAT3 may enhance anti-cancer immune responses and rescue the suppressed immunologic microenvironment in tumors. Taken together, STAT3 has emerged as a promising target in cancer immunotherapy.

The role of STAT3 in glioblastoma progression through dual influences on tumor cells and the immune microenvironment

Glioblastoma multiforme (GBM) is the most aggressive form of cancer that begins within the brain; generally, the patient has a dismal prognosis and limited therapeutic options. Signal transducer and activator of transcription 3 (STAT3) is a critical mediator of tumorigenesis, tumor progression, and suppression of anti-tumor immunity in GBM. In a high percentage of GBM cells and tumor microenvironments, persistent activation of STAT3 induces cell proliferation, anti-apoptosis, glioma stem cell maintenance, tumor invasion, angiogenesis, and immune evasion. This makes STAT3 an attractive therapeutic target and a prognostic indicator in GBM. Targeting STAT3 affords an opportunity to disrupt multiple pro-oncogenic pathways at a single molecular hub. Unfortunately, there are no successful STAT3 inhibitors currently in clinical trials. However, strong clinical evidence implicating STAT3 as a major factor in GBM justifies the identification of safe and effective strategies for inhibiting STAT3.

Cytokinesis Failure Leading to Chromosome Instability in v-Src-Induced Oncogenesis

v-Src, an oncogene found in Rous sarcoma virus, is a constitutively active variant of c-Src. Activation of Src is observed frequently in colorectal and breast cancers, and is critical in tumor progression through multiple processes. However, in some experimental conditions, v-Src causes growth suppression and apoptosis. In this review, we highlight recent progress in our understanding of cytokinesis failure and the attenuation of the tetraploidy checkpoint in v-Src-expressing cells. v-Src induces cell cycle changes—such as the accumulation of the 4N cell population—and increases the number of binucleated cells, which is accompanied by an excess number of centrosomes. Time-lapse analysis of v-Src-expressing cells showed that cytokinesis failure is caused by cleavage furrow regression. Microscopic analysis revealed that v-Src induces delocalization of cytokinesis regulators including Aurora B and Mklp1. Tetraploid cell formation is one of the causes of chromosome instability; however, tetraploid cells can be eliminated at the tetraploidy checkpoint. Interestingly, v-Src weakens the tetraploidy checkpoint by inhibiting the nuclear exclusion of the transcription coactivator YAP, which is downstream of the Hippo pathway and its nuclear exclusion is critical in the tetraploidy checkpoint. We also discuss the relationship between v-Src-induced chromosome instability and growth suppression in v-Src-induced oncogenesis.

Potential role for STAT3 inhibitors in glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor. Signal transducers and activators of transcription 3 (STAT3) is a transcription factor that translocates to the nucleus to modulate the expression of a variety of genes associated with cell survival, differentiation, proliferation, angiogenesis, and immune function. Several cancers induce constitutive STAT3 activation. Most studies have reported that STAT3 inhibition has antineoplastic activity; however, emerging evidence suggests that the role of STAT3 activity in GBM may be more nuanced than initially appreciated. The authors review the roles of STAT3 in GBM and discuss potential strategies for targeting STAT3.

Global tyrosine kinome profiling of human thyroid tumors identifies Src as a promising target for invasive cancers

BACKGROUND

Novel therapies are needed for the treatment of invasive thyroid cancers. Aberrant activation of tyrosine kinases plays an important role in thyroid oncogenesis. Because current targeted therapies are biased toward a small subset of tyrosine kinases, we conducted a study to reveal novel therapeutic targets for thyroid cancer using a bead-based, high-throughput system.

METHODS

Thyroid tumors and matched normal tissues were harvested from twenty-six patients in the operating room. Protein lysates were analyzed using the Luminex immunosandwich, a bead-based kinase phosphorylation assay. Data was analyzed using GenePattern 3.0 software and clustered according to histology, demographic factors, and tumor status regarding capsular invasion, size, lymphovascular invasion, and extrathyroidal extension. Survival and invasion assays were performed to determine the effect of Src inhibition in papillary thyroid cancer (PTC) cells.

RESULTS

Tyrosine kinome profiling demonstrated upregulation of nine tyrosine kinases in tumors relative to matched normal thyroid tissue: EGFR, PTK6, BTK, HCK, ABL1, TNK1, GRB2, ERK, and SRC. Supervised clustering of well-differentiated tumors by histology, gender, age, or size did not reveal significant differences in tyrosine kinase activity. However, supervised clustering by the presence of invasive disease showed increased Src activity in invasive tumors relative to non-invasive tumors (60% v. 0%, p<0.05). In vitro, we found that Src inhibition in PTC cells decreased cell invasion and proliferation.

CONCLUSION

Global kinome analysis enables the discovery of novel targets for thyroid cancer therapy. Further investigation of Src targeted therapy for advanced thyroid cancer is warranted.

Necdin, a negative growth regulator, is a novel STAT3 target gene down-regulated in human cancer

Cytokine and growth factor signaling pathways involving STAT3 are frequently constitutively activated in many human primary tumors, and are known for the transcriptional role they play in controlling cell growth and cell cycle progression. However, the extent of STAT3's reach on transcriptional control of the genome as a whole remains an important question. We predicted that this persistent STAT3 signaling affects a wide variety of cellular functions, many of which still remain to be characterized. We took a broad approach to identify novel STAT3 regulated genes by examining changes in the genome-wide gene expression profile by microarray, using cells expressing constitutively-activated STAT3. Using computational analysis, we were able to define the gene expression profiles of cells containing activated STAT3 and identify candidate target genes with a wide range of biological functions. Among these genes we identified Necdin, a negative growth regulator, as a novel STAT3 target gene, whose expression is down-regulated at the mRNA and protein levels when STAT3 is constitutively active. This repression is STAT3 dependent, since inhibition of STAT3 using siRNA restores Necdin expression. A STAT3 DNA-binding site was identified in the Necdin promoter and both EMSA and chromatin immunoprecipitation confirm binding of STAT3 to this region. Necdin expression has previously been shown to be down-regulated in a melanoma and a drug-resistant ovarian cancer cell line. Further analysis of Necdin expression demonstrated repression in a STAT3-dependent manner in human melanoma, prostate and breast cancer cell lines. These results suggest that STAT3 coordinates expression of genes involved in multiple metabolic and biosynthetic pathways, integrating signals that lead to global transcriptional changes and oncogenesis. STAT3 may exert its oncogenic effect by up-regulating transcription of genes involved in promoting growth and proliferation, but also by down-regulating expression of negative regulators of the same cellular processes, such as Necdin.

Pleiotropic action of AP-1 in v-Src-transformed cells

The activation of AP-1 is a hallmark of cell transformation by tyrosine kinases. In this study, we characterize the role of AP-1 proteins in the transformation of chicken embryo fibroblasts (CEF) by v-Src. In normal CEF, the expression of a dominant negative mutant of c-Jun (TAM67) induced senescence. In contrast, three distinct phenotypes were observed when TAM67 was expressed in v-Src-transformed CEF. While senescent cells were also present, the inhibition of AP-1 caused apoptosis in a fraction of the v-Src-transformed cells. In addition, cells containing lipid-rich vesicles accumulated, suggesting that a subpopulation of the v-Src-transformed cells underwent differentiation in response to the inhibition of AP-1. JunD and Fra-2 were the main components of this factor, while c-Jun accounted for a minor fraction of AP-1 in v-Src-transformed CEF. The downregulation of c-Jun expression by short hairpin RNA (shRNA) induced senescence in normal and v-Src-transformed cells. In contrast, a high incidence of apoptosis was caused by the downregulation of JunD, suggesting that it is required for the survival of v-Src-transformed CEF. Levels of the p53 tumor suppressor were elevated under conditions of JunD inhibition. Repression of p53 by shRNA enhanced the survival and anchorage-independent proliferation of v-Src-transformed CEF with JunD/AP-1 inhibition. The inhibition of Fra-2 had no visible phenotype in normal CEF but caused the appearance of lipid-rich vesicles in v-Src-transformed CEF. Therefore, AP-1 facilitated transformation by acting as a survival factor, by inhibiting premature entry into senescence, and by blocking the differentiation of v-Src-transformed CEF.

Silencing STAT3 with short hairpin RNA enhances radiosensitivity of human laryngeal squamous cell carcinoma xenografts in vivo

Short hairpin RNA (shRNA) targeting signal transducer and activator of transcription 3 (STAT3) potentiate the radiosensitivity of human laryngeal squamous carcinoma cells in vitro. In the present study, we investigated the inhibitory effect of STAT3 shRNA plus radiotherapy on nude mouse laryngeal squamous cell carcinoma xenografts. The xenotransplanted tumors were treated with STAT3 shRNA, with or without radiation, following a planned scheme. The inhibition rate for tumor growth was calculated and the tumor growth curve was plotted. In addition, the expression of p-STAT3, B cell lymphoma 2 (Bcl-2), p53, vascular endothelial growth factor (VEGF) protein and intratumoral microvessel density (MVD) was determined by immunohistochemistry. Flow cytometry was used to detect the rate of cell apoptosis. The results revealed that STAT3 shRNA transfection plus radiotherapy significantly minimized tumor volume and increased the rate of tumor inhibition. p-STAT3 protein expression and intratumoral MVD were observed to be down-regulated, whereas apoptosis was increased. There was a positive correlation between the expression of p-STAT3 and Bcl-2, and also between the expression of p53 and VEGF, and MVD. These findings indicate that STAT3 shRNA potentiate the radiosensitivity of laryngeal carcinoma xenografts in vivo by regulating downstream signaling proteins in the STAT3 pathway.

ErbB2-mediated Src and signal transducer and activator of transcription 3 activation leads to transcriptional up-regulation of p21Cip1 and chemoresistance in breast cancer cells

Overexpression of the ErbB2 receptor tyrosine kinase is prevalent in approximately 30% of human breast cancers and confers Taxol resistance. Our previous work has shown that ErbB2 inhibits Taxol-induced apoptosis in breast cancer cells by transcriptionally up-regulating p21(Cip1). However, the mechanism of ErbB2-mediated p21(Cip1) up-regulation is unclear. Here, we show that ErbB2 up-regulates p21(Cip1) transcription through increased Src activity in ErbB2-overexpressing cells. Src activation further activated signal transducer and activator of transcription 3 (STAT3) that recognizes a SIE binding site on the p21(Cip1) promoter required for ErbB2-mediated p21(Cip1) transcriptional up-regulation. Both Src and STAT3 inhibitors restored Taxol sensitivity in resistant ErbB2-overexpressing breast cancer cells. Our data suggest that ErbB2 overexpression can activate STAT3 through Src leading to transcriptional up-regulation of p21(Cip1) that confers Taxol resistance of breast cancer cells. Our study suggests a potential clinical application of Src and STAT3 inhibitors in Taxol sensitization of ErbB2-overexpressing breast cancers.

Transglutaminase-1 regulates renal epithelial cell proliferation through activation of Stat-3

Transglutaminase-1 (TGase-1) is a Ca(2+)-dependent enzyme capable of cross-linking a variety of proteins and promoting wound healing in the skin. In this study, we examined the role of TGase-1 in proliferation of renal proximal tubular cells (RPTC). TGase-1, but not TGase-2, -5, and -7, was expressed in RPTC. Treatment with monodansylcadarevine (MDC), a selective TGase inhibitor or down-regulation of TGase-1 with small interfering RNA (siRNA) decreased RPTC proliferation. Proliferation of RPTC was accompanied by activation of Akt and Stat-3 (signal transducer and activator of transcription-3). Treatment with MDC or TGase-1 siRNA decreased Stat-3 but not Akt phosphorylation. Further studies showed that the Janus-activated kinase 2 (JAK2) mediates phosphorylation of Stat-3, and knockdown of either JAK2 or Stat-3 by siRNA decreased RPTC proliferation. However, inhibition of TGase-1 decreased phosphorylation of Stat-3 but not JAK2. Overexpression of Stat-3, JAK2, and/or TGase-1 in RPTC revealed that JAK2 is indispensable for TGase-1 to induce Stat-3 phosphorylation and TGase-1 potentiates JAK2-induced Stat-3 phosphorylation. Consistent with these observations, we found that inhibition of TGase-1 and the JAK2-Stat-3 signaling pathway decreased the transcriptional activity of Stat-3 and expression of the Stat-3-targeted genes, cyclin D1 and cyclin E. Conversely, overexpresssion of TGase-1 enhanced the JAK2-dependent transcriptional activity of Stat-3. Finally, TGase-1 was found to interact with JAK2, and this interaction was inhibited by MDC. These results demonstrate that TGase-1 plays an important role in regulation of renal epithelial cell proliferation through the JAK2-Stat-3 signaling pathway.

PSM/SH2B1 splice variants: critical role in src catalytic activation and the resulting STAT3s-mediated mitogenic response

A role of PSM/SH2B1 had been shown in mitogenesis and extending to phenotypic cell transformation, however, the underlying molecular mechanism remained to be established. Here, four alternative PSM splice variants and individual functional protein domains were compared for their role in the regulation of Src activity. We found that elevated cellular levels of PSM variants resulted in phenotypic cell transformation and potentiated cell proliferation and survival in response to serum withdrawal. PSM variant activity presented a consistent signature pattern for any tested response of highest activity observed for gamma, followed by delta, alpha, and beta with decreasing activity. PSM-potentiated cell proliferation was sensitive to Src inhibitor herbimycin and PSM and Src were found in the same immune complex. PSM variants were substrates of the Src Tyr kinase and potentiated Src catalytic activity by increasing the V(max) and decreasing the K(m) for ATP with the signature pattern of variant activity. Dominant-negative PSM peptide mimetics including the SH2 or PH domains inhibited Src catalytic activity as well as Src-mediated phenotypic cell transformation. Activation of major Src substrate STAT3 was similarly potentiated by the PSM variants in a Src-dependent fashion or inhibited by PSM domain-specific peptide mimetics. Expression of a dominant-negative STAT3 mutant blocked PSM variant-mediated phenotypic cell transformation. Our results implicate an essential role of the PSM variants in the activation of the Src kinase and the resulting mitogenic response--extending to phenotypic cell transformation and involving the established Src substrate STAT3.

Inflammation and lung carcinogenesis: applying findings in prevention and treatment

Lung carcinogenesis is a complex process requiring the acquisition of genetic mutations that confer the malignant phenotype as well as epigenetic alterations that may be manipulated in the course of therapy. Inflammatory signals in the lung cancer microenvironment can promote apoptosis resistance, proliferation, invasion, metastasis, and secretion of proangiogenic and immunosuppressive factors. Here, we discuss several prototypical inflammatory mediators controlling the malignant phenotype in lung cancer. Investigation into the detailed molecular mechanisms underlying the tumor-promoting effects of inflammation in lung cancer has revealed novel potential drug targets. Cytokines, growth factors and small-molecule inflammatory mediators released in the developing tumor microenvironment pave the way for epithelial-mesenchymal transition, the shift from a polarized, epithelial phenotype to a highly motile mesenchymal phenotype that becomes dysregulated during tumor invasion. Inflammatory mediators within the tumor microenvironment are derived from neoplastic cells as well as stromal and inflammatory cells; thus, lung cancer develops in a host environment in which the deregulated inflammatory response promotes tumor progression. Inflammation-related metabolic and catabolic enzymes (prostaglandin E(2) synthase, prostaglandin I(2) synthase and 15-hydroxyprostaglandin dehydrogenase), cell-surface receptors (E-type prostaglandin receptors) and transcription factors (ZEB1, SNAIL, PPARs, STATs and NF-kappaB) are differentially expressed in lung cancer cells compared with normal lung epithelial cells and, thus, may contribute to tumor initiation and progression. These newly discovered molecular mechanisms in the pathogenesis of lung cancer provide novel opportunities for targeted therapy and prevention in lung cancer.

Delineating v-Src downstream effector pathways in transformed myoblasts

In this study, we delineate the intracellular signalling pathways modulated by a conditional v-Src tyrosine kinase that lead to unrestrained proliferation and block of differentiation of primary avian myoblasts. By inhibiting Ras-MAPK kinase and phosphatidylinositol 3-kinase with different means, we find that both pathways play crucial roles in controlling v-Src-sustained growth factor and anchorage independence for proliferation. The Ras-MAPK kinase pathway also contributes to block of differentiation independently of cell proliferation since inhibition of this pathway both in proliferating and growth-arrested v-Src-transformed myoblasts induces expression of muscle-specific genes, fusion into multinucleated myotubes and assembly of specialized contractile structures. Importantly, we find that the p38 MAPK pathway is inhibited by v-Src in myoblasts and its forced activation results in growth inhibition and expression of differentiation, indicating p38 MAPK as a critical target of v-Src in growth transformation and myogenic differentiation. Furthermore, we show that downregulation of p38 MAPK activation may occur via Ras-MAPK kinase, thus highlighting a cross-regulation between the two pathways. Finally, we report that the simultaneous inhibition of MAPK kinase and calpain, combined to activation of p38 MAPK, are sufficient to reconstitute largely the differentiation potential of v-Src-transformed myoblasts.

Crosstalk between cancer and immune cells: role of STAT3 in the tumour microenvironment

Immune cells in the tumour microenvironment not only fail to mount an effective anti-tumour immune response, but also interact intimately with the transformed cells to promote oncogenesis actively. Signal transducer and activator of transcription 3 (STAT3), which is a point of convergence for numerous oncogenic signalling pathways, is constitutively activated both in tumour cells and in immune cells in the tumour microenvironment. Constitutively activated STAT3 inhibits the expression of mediators necessary for immune activation against tumour cells. Furthermore, STAT3 activity promotes the production of immunosuppressive factors that activate STAT3 in diverse immune-cell subsets, altering gene-expression programmes and, thereby, restraining anti-tumour immune responses. As such, STAT3 propagates several levels of crosstalk between tumour cells and their immunological microenvironment, leading to tumour-induced immunosuppression. Consequently, STAT3 has emerged as a promising target for cancer immunotherapy.

Update on HIV-associated nephropathy

PURPOSE OF REVIEW

HIV-associated nephropathy is characterized by a constellation of pathologic findings including a collapsing glomerulopathy, tubular dilatation, and interstitial infiltration with leukocytes. This review summarizes some of the recent advances in our understanding of the gene products and signaling pathways that contribute to the pathogenesis of HIV-associated nephropathy.

RECENT FINDINGS

Podocytes infected with HIV-associated nephropathy exhibit podocyte proliferation and de-differentiation. Restriction of HIV-1 transgene expression to the podocyte in a murine model supports the belief that podocyte infection is pivotal to the development of the disease. Recent studies have provided compelling in-vitro and in-vivo evidence that expression of the HIV-1 accessory gene nef is critical in altering the phenotype of mature podocytes and causing injury to these cells. An in-vitro study suggests that nef's effects in the podocyte appear to be mediated through Src kinase-dependent activation of the signal transducer and activator of transcription 3 and mitogen-activated protein kinase 1,2 signaling pathways.

SUMMARY

Recent evidence demonstrates that the viral protein nef plays a critical role in the development of HIV-associated nephropathy and provides a foundation for developing new therapeutic strategies for patients afflicted with this disease.

Cyclooxygenase-2-dependent activation of signal transducer and activator of transcription 3 by interleukin-6 in non-small cell lung cancer

PURPOSE

Cyclooxygenase-2 (COX-2), phosphorylated signal transducers and activators of transcription 3 (STAT3), and interleukin-6 (IL-6) are elevated in non-small cell lung cancer (NSCLC). These molecules affect numerous cellular pathways, including angiogenesis and apoptosis resistance, and, therefore, may act in concert in NSCLC.

EXPERIMENTAL DESIGN

We examined IL-6 and phosphorylated STAT3 in COX-2-overexpressing [COX-2 sense-oriented (COX-2-S)] NSCLC cells and control cells. The effect of IL-6, STAT3, phosphatidylinositol 3-kinase, and mitogen-activated protein/extracellular signal-regulated kinase kinase on vascular endothelial growth factor (VEGF) production and apoptosis resistance was assessed in COX-2-overexpresing cells.

RESULTS

We report that NSCLC cells overexpressing COX-2 (COX-2-S) have increased IL-6 and phosphorylated STAT3 expression compared with control cells. IL-6 induced expression of VEGF in NSCLC cells. Moreover, blocking IL-6, mitogen-activated protein/extracellular signal-regulated kinase kinase, or phosphatidylinositol 3-kinase decreased VEGF production in COX-2-S cells. The addition of IL-6 to NSCLC cells resulted in increased apoptosis resistance. Furthermore, the inhibition of STAT3 or IL-6 induced apoptosis and reduced survivin expression, a member of the inhibitor of apoptosis protein family in COX-2-S cells.

CONCLUSIONS

Overall, these findings suggest a novel pathway in which COX-2 activates STAT3 by inducing IL-6 expression. This pathway could contribute to tumor formation by promoting survivin-dependent apoptosis resistance and VEGF production. These findings provide a rationale for the future development of STAT3, IL-6, and/or COX-2-targeted therapies for the treatment of lung cancer.

Constitutive activation of JAK3/STAT3 in colon carcinoma tumors and cell lines: inhibition of JAK3/STAT3 signaling induces apoptosis and cell cycle arrest of colon carcinoma cells

Signal transducer and activator of transcription 3 (STAT3) has oncogenic potential. The biological effects of STAT3 have not been studied extensively in the pathogenesis of colon cancer, nor has the role of Janus kinase 3 (JAK3), the physiological activator of STAT3, been evaluated. Here, we demonstrate that activated STAT3 (pSTAT3) and activated JAK3 (pJAK3) are expressed constitutively in two colon cancer cell lines, SW480 and HT29. To evaluate the significance of JAK3/STAT3 signaling, we inhibited JAK3 with AG490 and STAT3 with a dominant-negative construct. Inhibition of JAK3 down-regulated pSTAT3. The blockade of JAK3/STAT3 signaling significantly decreased viability of colon cancer cells due to apoptosis and cell-cycle arrest through down-regulation of Bcl-2, Bcl-X(L), Mcl-1, and cyclin D2 and up-regulation of p21(waf1/cip1) and p27(kip1). We also examined histological sections from 22 tumors from patients with stage II or stage IV colon cancer and found STAT3, JAK3, and their activated forms to be frequently expressed. Furthermore, quantitative reverse transcriptase-polymerase chain reaction identified JAK3 mRNA in colon cancer cell lines and primary tumors. Our findings illustrate the biological importance of JAK3/STAT3 activation in the oncogenesis of colon cancer and provide novel evidence that JAK3 is expressed and contributes to STAT3 activation in this malignant neoplasm.

Bcl-2 but not clusterin/apolipoprotein J protected human diploid fibroblasts and immortalized keratinocytes from ceramide-induced apoptosis: role of p53 in the ceramide response

The role of clusterin/apolipoprotein J (Clu/ApoJ) and Bcl-2 on C(2)-ceramide-induced apoptosis of embryonic human diploid fibroblasts, MRC-5 and immortalized adult skin keratinocytes, HaCaT was investigated. C(2)-ceramide-induced apoptosis of HaCaT in a time- and dose-dependent manner, while in MRC-5 only at higher concentrations. There was a dose-dependent accumulation of Clu/ApoJ and downregulation of Bcl-2 which correlated with C(2)-ceramide-induced apoptosis of MRC-5. While overexpression of Bcl-2 suppressed C(2)-ceramide-mediated apoptosis in both cell types, Clu/ApoJ failed to do so, accessed by morphological changes, DNA fragmentation and PARP cleavage. There was no change in the expression of endogenous p53 or p21(Waf1/Cip1) upon C(2)-ceramide treatment of MRC-5. However, mutant p53(143ala) increased the sensitivity of MRC-5 to C(2)-ceramide-induced apoptosis by markedly downregulating Bcl-2, pointing to a role for p53. These results suggested that whereas downregulation of Bcl-2 may be a crucial factor involved in C(2)-ceramide-induced apoptosis, accumulation of Clu/ApoJ may be a signal of stress response. Moreover, the ceramide-activated apoptotic pathway may be regulated by p53.

Enhanced v-Src-induced oncogenic transformation in the absence of focal adhesion kinase is mediated by phosphatidylinositol 3-kinase

We showed previously [K. Moissoglu, I.H. Gelman, J. Biol. Chem. 278 (2003) 47946-47959] that oncogenic v-Src could induce 7- to 10-fold greater anchorage-independent growth (AIG) in FAK-null mouse embryo fibroblasts (MEF) compared to those expressing FAK. Here, we demonstrate that the enhanced AIG (eAIG) correlates with increased activation levels of phosphatidylinositol 3-kinase (PI3K) and not with changes in the protein levels of the p85 regulatory subunit of PI3K, PDK1 or PTEN- modulators, and/or mediators of PI3K activity. eAIG could be blunted selectively by treatment with the PI3K inhibitor, LY294002, or by overexpression of either the PI3K antagonist, PTEN, dominant-interfering alleles of PI3K or a downstream PI3K mediator, AKT, but not by the MEK inhibitor, PD98059, dominant-interfering alleles of MEK or the signal transducer and activator of transcription (STAT)-3. In contrast, RNAi-mediated knockdown of FAK resulted in increased v-Src-induced AIG. Expression of a constitutively active PI3K allele was sufficient to induce higher levels of AIG, whereas overexpression of v-Src produced only larger-sized colonies in soft agar. Interestingly, FAK was required for full activation of PI3K by PDGF whereas the activation of PI3K by insulin was significantly increased in FAK-/- cells. Thus, although FAK is dispensable for v-Src-induced oncogenic transformation in vitro, it may exert either positive or negative effects on signaling or motility depending on which pathways are activated in cancer cells.

Induction of genes involved in cell cycle progression by interleukin-4

Interleukin-4 (IL-4) can elicit diverse cellular responses, including differentiation, fusion, and proliferation, and these are all critical to establishment of an effective immune response. In this report, we provide evidence that IL-4 induces the proliferation of T lymphocytes with the coordinate transcriptional induction of the cell cycle regulatory genes encoding Cdc25A and the minichromosome maintenance (MCM) family. This specific gene induction appears to be due to activation of the signal transducer and activator of transcription, Stat6, and in part to phosphatidylinositol 3-kinase (PI3K). The function of another family of transcription factors, E2F, is known to induce cell cycle-regulated gene expression by binding to specific DNA target sites. We demonstrate that IL-4-activated Stat6 dimers can bind to a subset of E2F target sites and stimulate gene expression by binding to these DNA elements. Our results support a role for the Stat6 signal pathway in regulating a subset of E2F-responsive genes. In addition, activation of PI3K may play a complementary role in the induction of cell cycle-regulated genes in response to IL-4.

AND-34 Activates Phosphatidylinositol 3-Kinase and Induces Anti-Estrogen Resistance in a SH2 and GDP Exchange Factor–Like Domain-Dependent Manner

AND-34, a 95-kDa protein with modest homology to Ras GDP exchange factors, associates with the focal adhesion protein p130Cas. Overexpression of AND-34 confers anti-estrogen resistance in breast cancer cell lines, a property linked to its ability to activate Rac. Here, we show that both the GDP exchange factor–like domain and the SH2 domain of AND-34 are required for Rac activation and for resistance to the estrogen receptor (ER) antagonist ICI 182,780. As phosphatidylinositol 3-kinase (PI3K) signaling can regulate Rac activation, we examined the effects of AND-34 on PI3K. Overexpression of AND-34 in MCF-7 cells increased PI3K activity and augmented Akt Ser473 phosphorylation and kinase activity. Inhibition of PI3K with LY294002 or a dominant-negative p85 construct blocked AND-34-mediated Rac and Akt activation. Although R-Ras can activate PI3K, transfection with constitutively active R-Ras failed to induce Rac activation and AND-34 overexpression failed to induce R-Ras activation. Treatment of either vector-only or AND-34-transfected ZR-75-1 cells with ICI 182,780 markedly diminished ERα levels, suggesting that AND-34-induced anti-estrogen resistance is likely to occur by an ERα-independent mechanism. Treatment of a ZR-75-1 breast cancer cell line stably transfected with AND-34 plus 2 μmol/L LY294002 or 10 μmol/L NSC23766, a Rac-specific inhibitor, abrogated AND-34-induced resistance to ICI 182,780. Our studies suggest that AND-34-mediated PI3K activation induces Rac activation and anti-estrogen resistance in human breast cancer cell lines.

Role of STATs as downstream signal transducers in Src family kinase-mediated tumorigenesis

The signal transducers and activators of transcription (STATs) were originally identified in the signaling pathway activated by the nontyrosine kinase containing cytokine receptors. The role of these STATs in hematopoietic cell signaling has been well described. In the case of cytokine receptors, activation of STAT tyrosine phosphorylation occurs through ligand-induced recruitment, and activation of the intracellular JAK kinases. However, STATs can also be activated by growth factor receptors, particularly the EGFR; as well as by members of the Src Family of Kinases (SFKs), particularly c-Src. In many cases, there is a differential activation of the STATs by these tyrosine kinases as compared to activation by the cytokine receptors. This difference provides for the potential of unique actions of STATs in response to growth factor receptor and SFK activation. Since there are many cancers in which SFKs and c-Src in particular, are co-overexpressed with growth factor receptors, it is not surprising that STATs play an important role in the tumorigenesis process induced by c-Src. The activation paradigm and role of STATs in these cancers, with particular emphasis on breast cancer models, is discussed.

Newest findings on the oldest oncogene; how activated src does it

Oncogenic forms of the non-receptor tyrosine kinase Src alter cell structure, in particular the actin cytoskeleton and the adhesion networks that control cell migration, and also transmit signals that regulate proliferation and cell survival. Recent work indicates that they do so by influencing the RhoA-ROCK pathway that controls contractile actin filament assembly, the STAT family of transcription factors needed for transformation, and the Cbl ubiquitin ligase that controls Src protein levels. These studies also shed light on the role of focal adhesion kinase (FAK) downstream of v-Src and other signalling pathways in controlling migration, invasion and survival of transformed cells. Src directly phosphorylates integrins and can also modulate R-Ras activity. Moreover, it stimulates the E-cadherin regulator Hakai, interacts with and phosphorylates the novel podosome-linked adaptor protein Fish, and progressively phosphorylates the gap junction component connexion 43. A recurring theme is the identification of novel and important Src substrates that mediate key biological events associated with transformation.

Nef stimulates proliferation of glomerular podocytes through activation of Src-dependent Stat3 and MAPK1,2 pathways

In collapsing focal segmental glomerulosclerosis (FSGS) of HIV-associated nephropathy (HIVAN), podocytes exhibit a high proliferation rate and loss of differentiation markers. We have found previously that the nef gene of HIV-1 is responsible for these changes. Here, we investigated the signaling pathways induced by Nef and its role in the pathogenesis of HIVAN. Using conditionally immortalized podocytes after differentiation, we found that infection of podocytes with nef increased Src kinase activity and signal transducer and activator of transcription 3 (Stat3) phosphorylation and activated the Ras-c-Raf-MAPK1,2 pathway. A dominant negative mutant of Src abolished the Nef effect, whereas inhibition of MAPK1,2 or dominant negative Stat3 reduced Nef effects partially. Reducing the expression of Nef with small interference RNA reversed the Nef effect. Mutation of Nef in the PxxP or R105R106 motifs diminished Nef signaling and the phenotypic changes in podocytes. Both phospho-MAPK1,2 and phospho-Stat3 staining increased in podocytes of kidneys from HIV-1 transgenic mice compared with their littermates and in podocytes of kidneys from HIVAN patients compared with HIV patients with non-HIVAN kidney diseases or non-HIV patients with idiopathic FSGS, classic FSGS, or minimal-change disease. These data suggest that Nef-induced activation of Stat3 and Ras-MAPK1,2 via Src-dependent pathways is responsible for podocyte proliferation and dedifferentiation, a characteristic finding in collapsing FSGS of HIVAN.

Identification of a cytokine-induced antiapoptotic molecule anamorsin essential for definitive hematopoiesis

Many growth factors and cytokines prevent apoptosis. Using an expression cloning method, we identified a novel antiapoptotic molecule named Anamorsin, which does not show any homology to known apoptosis regulatory molecules such as Bcl-2 family, caspase family, or signal transduction molecules. The expression of Anamorsin was completely dependent on stimulation with growth factors such as interleukin 3, stem cell factor, and thrombopoietin in factor-dependent hematopoietic cell lines, and forced expression of Anamorsin conferred resistance to apoptosis caused by growth factor deprivation in vitro. Furthermore, Anamorsin was found to act as an antiapoptotic molecule in vivo because Anamorsin^−/− mice die in late gestation due to defective definitive hematopoiesis in the fetal liver (FL). Although the number of hematopoietic stem/progenitor cells in the FL did not decrease in these mice, myeloid, and particularly erythroid colony formation in response to cytokines, was severely disrupted. Also, Anamorsin^−/− erythroid cells initiated apoptosis during terminal maturation. As for the mechanism of Anamorsin-mediated cell survival, a microarray analysis revealed that the expression of Bcl-xL and Jak2 was severely impaired in the FL of Anamorsin^−/− mice. Thus, Anamorsin is considered to be a necessary molecule for hematopoiesis that mediates antiapoptotic effects of various cytokines.

Signal transducer and activator of transcription 3 activation by the delta-opioid receptor via Galpha14 involves multiple intermediates

The hematopoietic-specific Galpha14 links a variety of G protein-coupled receptors to phospholipase Cbeta (PLCbeta) stimulation. Recent studies reveal that several Galpha subunits are capable of activating signal transducer and activator of transcription (STAT) proteins. In the present study, we investigated the mechanism by which Galpha14 mediates receptor-induced stimulation of STAT3. In human embryonic kidney 293 cells, coexpression of Galpha14 with delta-opioid receptor supported [D-Pen2, D-Pen5]enkephalin (DPDPE)-induced STAT3 phosphorylations at both Tyr705 and Ser727 in a pertussis toxin-insensitive manner. The constitutively active Galpha4QL mutant also induced STAT3 phosphorylations at these sites and promoted STAT3-dependent luciferase activity. Requirements for PLCbeta, protein kinase C (PKC), and calmodulin-dependent kinase II (CaMKII) in Galpha14QL-induced STAT3 activation were demonstrated by their respective inhibitors as well as by coexpression of their dominant-negative mutants. Inhibition of c-Src and Janus kinase 2 and 3 activities abolished STAT3 activation induced by Galpha14QL, but no physical association between Galpha14QL and c-Src could be detected by coimmunoprecipitation. Various intermediates along the extracellular signal-regulated kinase signaling cascade were apparently required for Galpha14QL-induced STAT3 activation; they included Ras/Rac1, Raf-1, and mitogen-activated protein kinase kinase-1/2. In contrast, functional blockade of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol-3 kinase had no effect on Galpha14QL-induced responses. PLCbeta, PKC, and CaMKII were shown to be involved in Galpha14QL-mediated c-Src phosphorylation. Similar results were obtained with human erythro-leukemia cells upon DPDPE treatment. These results demonstrate for the first time that Galpha14 activation can lead to STAT3 stimulation via a complex signaling network involving multiple intermediates.

Blockade of v-Src-stimulated tumor formation by the Src homology 3 domain of Crk-associated substrate (Cas)

Crk-associated substrate (Cas) is highly phosphorylated by v-Src and plays a critical role in v-Src-induced cell transformation. In this study, we found that the Src homology (SH) 3 domain of Cas blocked v-Src-stimulated anchorage-independent cell growth, Matrigel invasion, and tumor growth in nude mice. Biochemical analysis revealed that the Cas SH3 domain selectively inhibited v-Src-stimulated activations of AKT and JNK, but not ERK and STAT3. Attenuation of the AKT pathway by the Cas SH3 domain rendered v-Src-transformed cells susceptible to apoptosis. Inhibition of the JNK pathway by the Cas SH3 domain led to suppression of v-Src-stimulated invasion. Taken together, our results indicate that the Cas SH3 domain has an anti-tumor function, which severely impairs the transforming potential of v-Src.

An increase in the expression and total activity of endogenous p60(c-Src) in several factor-independent mutants of a human GM-CSF-dependent leukemia cell line (TF-1)

Growth factor independence of hematopoietic cells can be induced by ectopic expression of a variety of oncogenes encoding receptor or cytoplasmic tyrosine kinases. To examine whether the activation of tyrosine kinases occurs in factor-independent mutants in vivo, the tyrosine-phosphorylated proteins from 14 factor-independent mutants of a GM-CSF-dependent cell line (TF-1) were analysed. These mutants did not secrete any growth-stimulating activity for TF-1 cells, suggesting that activation of intracellular signaling rather than an autocrine stimulation by secreted growth factors is responsible for their factor-independent growth. In 11 out of 14 GM-CSF-independent mutants analysed, a constitutively tyrosine-phosphorylated protein of 60 kDa was detected, which was subsequently identified as p60(c-Src). The kinase activity of p60(c-Src) was increased up to 12-fold in these mutants, which was at least in part due to overexpression of the c-src gene on the RNA and protein level. The Src substrate Sam68 showed an increased phosphorylation in mutants with high Src activity, suggesting that p60(c-Src) triggers downstream signaling in these cells. Treatment of the factor-independent mutants with the Src kinase inhibitor PP2 resulted in a reduced proliferation, demonstrating that Src kinases are essential for these cells for maximal proliferation. Further analysis of factor-independent mutants with low or undetectable Src activity revealed a constitutive phosphorylation of the common beta chain of the GM-CSF receptor and STAT5. Our data indicate an increase in the expression and total activity of endogenous p60(c-Src) in several GM-CSF-independent TF-1 mutants, further underlining the role of Src in the process of autonomous growth of hematopoietic cells.

Leukotriene D4 mediates survival and proliferation via separate but parallel pathways in the human intestinal epithelial cell line Int 407

We demonstrated previously that leukotriene D4 (LTD4) regulates proliferation of intestinal epithelial cells through a CysLT receptor by protein kinase C (PKC)epsilon-dependent stimulation of the mitogen-activated protein kinase ERK1/2. Our current study provides the first evidence that LTD4 can activate 90-kDa ribosomal S6 kinase (p90RSK) and cAMP-responsive element-binding protein (CREB) via pertussis-toxin-sensitive Gi protein pathways. Transfection and inhibitor experiments revealed that activation of p90RSK, but not CREB, is a PKCepsilon/Raf-1/ERK1/2-dependent process. LTD4-mediated CREB activation was not affected by expression of kinase-dead p90RSK but was abolished by transfection with the regulatory domain of PKCalpha (a specific dominant-inhibitor of PKCalpha). Kinase-negative mutants of p90RSK and CREB (K-p90RSK and K-CREB) blocked the LTD4-induced increase in cell number and DNA synthesis (thymidine incorporation). Compatible with these results, flow cytometry showed that LTD4 caused transition from the G0/G1 to the S+G2/M cell cycle phase, indicating increased proliferation. Similar treatment of cells transfected with K-p90RSK resulted in cell cycle arrest in the G0/G1 phase, consistent with a role of p90RSK in LTD4-induced proliferation. On the other hand, expression of K-CREB caused a substantial buildup in the sub-G0/G1 phase, suggesting a role for CREB in mediating LTD4-mediated survival in intestinal epithelial cells. Our results show that LTD4 regulates proliferation and survival via distinct intracellular signaling pathways in intestinal epithelial cells.

Synergistic cooperation between the AP-1 and LEF-1 transcription factors in activation of the matrilysin promoter by the src oncogene: implications in cellular invasion

The matrix metalloprotease matrilysin is expressed in premalignant polyps and plays a key role in local invasion during the progression of digestive tumors. In the present work, we investigated the possible relationships between the activity of the mouse and human matrilysin promoters (Mp), endogenous matrilysin protein expression, and two early oncogenetic defects frequently observed in human colonic cancers, namely activation of the src oncogene and impairment of the Wnt/APC/beta-catenin pathway. Using transient transfection assays, we report here that src signaling and the HMG-box transcription factor LEF-1 act synergistically with the proximal (-61 to -67) AP-1 binding site to transactivate the Mp in premalignant and tumorigenic kidney and colonic epithelial cells, through beta-catenin- and axin-independent signaling pathways. This synergism involves the -109 and -194 Tcf/LEF-1 binding sites in the Mp and a physical interaction between LEF-1 and c-Jun. Furthermore, src coordinates accumulation of the c-Jun factor and matrilysin transcripts. Conversely, the c-Jun dominant negative mutant TAM67 and the src tyrosine kinase inhibitor M475271 impaired src-induced Mp activation, matrilysin protein accumulation, and invasion of type I collagen gels. This mechanism may thereby contribute to cellular invasion during the early-stage adenoma/adenocarcinoma conversion and the metastatic process of digestive tumors.

Activation of Stat3 by receptor tyrosine kinases and cytokines regulates survival in human non-small cell carcinoma cells

Overexpression of receptor tyrosine kinases including the epidermal growth factor receptor (EGF-R) as well as nonreceptor tyrosine kinases, such as Src, have been implicated in the formation of human lung cancers. In addition, cytokines like interleukin-6 (IL-6) have been demonstrated to modulate lung cancer cell growth and elevated levels of IL-6 have been shown to be an adverse prognostic factor for patients with lung cancer. Despite a large body of evidence pointing to their potential importance, few direct studies into the role of signal transducers and activators of transcription (STAT) pathways in human lung cancer have been undertaken. Here we demonstrate that multiple nonsmall cell lung cancer cell lines demonstrate constitutive Stat3 DNA-binding activity. Stat3 DNA-binding activity is specifically upregulated by the addition of epidermal growth factor (EGF), IL-6, and hepatocyte-derived growth factor (HGF). Furthermore, the stimulation of Stat3 DNA-binding activity by EGF requires the activity of EGF-R tyrosine kinase as well as Src-kinase, while the upregulation of Stat3 activity by IL-6 or HGF requires only Src-kinase activity. Treatment of A549 lung cancer cells with PD180970 or SU6656, both pharmacological inhibitors of Src-kinase, resulted in reduced Src and Stat3 activity, cell cycle arrest in G2, and reduced viability of cells accompanied by induction of apoptosis. Treatment of Stat3-positive A549 and H358 cells with antisense Stat3 oligonucleotides results in complete loss of Stat3 DNA-binding activity and apoptosis, while Stat3-positive H1299 cells remained healthy. Finally, an adenoviral vector expressing a dominant-negative Stat3 isoform results in loss of Stat3 DNA-binding activity, apoptosis, and reduced cellular viability. These results demonstrate a role of Stat3 in transducing survival signals downstream of tyrosine kinases such as Src, EGF-R, and c-Met, as well as cytokines such as IL-6, in human nonsmall cell lung cancers.

Opposing effects of PML and PML/RAR alpha on STAT3 activity

Promyelocytic leukemia protein PML acts as a tumor suppressor, whereas its chimeric mutant promyelocytic leukemia/retinoic acid receptor alpha (PML/RAR alpha) causes acute promyelocytic leukemia (APL). Because PML has been shown to form transcription-regulatory complexes with various molecules, we speculated that PML and/or PML/RAR alpha might affect signal transducer and activator of transcription 3 (STAT3) activity, which plays a crucial role in granulocyte colony-stimulating factor (G-CSF)-induced growth and survival of myeloid cells. In luciferase assays, PML inhibited STAT3 activity in NIH3T3, 293T, HepG2, and 32D cells. PML formed a complex with STAT3 through B-box and COOH terminal regions in vitro and in vivo, thereby inhibiting its DNA binding activity. Although PML/RAR alpha did not interact with STAT3, it dissociated PML from STAT3 and restored its activity suppressed by PML. To assess the biologic significance of these findings, we introduced PML and PML/RAR alpha into interleukin-3 (IL-3)-dependent Ba/F3 cells expressing the chimeric receptor composed of extracellular domain of G-CSF-R and cytoplasmic domain of gp130, in which gp130-mediated growth is essentially dependent on STAT3 activity. Neither PML nor PML/RAR alpha affected IL-3-dependent growth of these clones. By contrast, gp130-mediated growth was abrogated by PML, whereas it was enhanced by PML/RAR alpha. These results reveal new functions of PML and PML/RAR alpha and suggest that dysregulated STAT3 activity by PML/RAR alpha may participate in the pathogenesis of APL.

FRNK blocks v-Src-stimulated invasion and experimental metastases without effects on cell motility or growth

Focal adhesion kinase (FAK) was first identified as a viral Src (v-Src) substrate, but the role of FAK in Src transformation events remains undefined. We show that stable expression of the FAK C-terminal domain (termed FRNK) in v-Src-transformed NIH 3T3 fibroblasts inhibited cell invasion through Matrigel and blocked experimental metastases in nude mice without effects on cell motility. FRNK inhibitory activity was dependent upon its focal contact localization. FRNK expression disrupted the formation of a v-Src-FAK signaling complex, inhibited p130Cas tyrosine phosphorylation, and attenuated v-Src-stimulated ERK and JNK kinase activation. However, FRNK did not affect v-Src-stimulated Akt activation, cell growth in soft agar, or subcutaneous tumor formation in nude mice. FRNK-expressing cells exhibited decreased matrix metalloproteinase-2 (MMP-2) mRNA levels and MMP-2 secretion. Transient FRNK expression in human 293 cells inhibited exogenous MMP-2 promoter activity and overexpression of wild-type but not catalytically-inactive (Ala-404) MMP-2 rescued v-Src-stimulated Matrigel invasion in the presence of FRNK. Our findings show the importance of FAK in Src-stimulated cell invasion and support a role for Src-FAK signaling associated with elevated tumor cell metastases.

Pharmacogenomic strategies for developing customized chemotherapy in non-small cell lung cancer

In this review, we deal with six groups of cytotoxic drugs commonly used in the treatment of non-small cell lung cancer (NSCLC). Although there are many reviews of thymidylate synthase (TS) and antifolate inhibitors, in this article, we have tried to highlight aspects that are more important for medical oncologists to consider when treating NSCLC patients. There is compelling evidence that TS gene transcripts and TS polymorphisms could be used to decide which patients can best benefit from adjuvant chemotherapy approaches, especially in colorectal cancer, and not less importantly, to tailor chemotherapy in metastatic NSCLC when using drugs akin to fluorouracil, such as pemetrexed. Secondly, cisplatin is central to chemotherapy combinations and evidence indicates that DNA repair capacity influences response to cisplatin-based regimens. ERCC1 gene transcript stands out as a predictive marker of cisplatin sensitivity. Thirdly, preliminary studies indicate that upregulation of beta-tubulin III correlates with response to paclitaxel and vinorelbine. Fourthly, overexpression of ribonucleotide reductase can influence response to gemcitabine. Fifthly, we describe mechanisms of resistance to topoisomerase I inhibitors, although this subject has not yet been completely elucidated. Finally, to understand the mechanisms of resistance to EGF-R inhibitors, which have been shown to be useful in many different types of cancer, the Src-STAT signaling pathways are described here in detail. Hopefully, the assessment of Src and of STAT-3 can be implemented as predictive markers.

Identification of Src transformation fingerprint in human colon cancer

We used a classical rodent model of transformation to understand the transcriptional processes, and hence the molecular and cellular events a given cell undergoes when progressing from a normal to a transformed phenotype. Src activation is evident in 80% of human colon cancer, yet the myriad of cellular processes effected at the level of gene expression has yet to be fully documented. We identified a Src 'transformation fingerprint' within the gene expression profiles of Src-transformed rat 3Y1 fibroblasts demonstrating a progression in transformation characteristics. To evaluate the role of this gene set in human cancer development and progression, we extracted the orthologous genes present on the Affymetrix Hu95A GeneChip (12k named genes) and compared expression profiles between the Src-induced rodent cell line model of transformation and staged colon tumors where Src is known to be activated. A similar gene expression pattern between the cell line model and staged colon tumors for components of the cell cycle, cytoskeletal associated proteins, transcription factors and lysosomal proteins suggests the need for co-regulation of several cellular processes in the progression of cancer. Genes not previously implicated in tumorigenesis were detected, as well as a set of 14 novel, highly conserved genes with here-to-fore unknown function. These studies define a set of transformation associated genes whose up-regulation has implications for understanding Src mediated transformation and strengthens the role of Src in the development and progression of human colon cancer. Supportive Supplemental Data can be viewed at http://pga.tigr.org/PGApubs.shtml.

Leukotriene D(4) activates MAPK through a Ras-independent but PKCepsilon-dependent pathway in intestinal epithelial cells

We have recently shown that leukotriene D(4) (LTD(4)) increases cell survival in intestinal epithelial cells. Here we report and explore the complementary finding that LTD(4) also enhances proliferation in these cells. This proliferative response was approximately half of that induced by epidermal growth factor (EGF) and its required activation of protein kinase C (PKC), Ras and the mitogen-activated protein kinase (MAPK) Erk-1/2. EGF also activated Erk-1/2 in these cells; however the EGF-receptor inhibitor PD153035 did not affect the LTD(4)-induced activation of Erk-1/2. In addition, LTD(4) did not induce phosphorylation of the EGF receptor, nor did pertussis toxin (PTX) block EGF-induced activation of Erk-1/2, thus refuting a possible crosstalk between the receptors. Furthermore, LTD(4)-induced, but not EGF-induced, activation of Erk-1/2 was sensitive to PTX, PKC inhibitors and downregulation of PKCepsilon. A definite role for PKCepsilon in LTD(4)-induced stimulation of Erk-1/2 was documented by the inability of LTD(4) to activate Erk-1/2 in cells transfected with either the regulatory domain of PKCepsilon (an isoform specific dominant-negative inhibitor) or a kinase-dead PKCepsilon. Although Ras and Raf-1 were both transiently activated by LTD(4), only Raf-1 activation was abolished by abrogation of the PKC signal. Furthermore, the LTD(4)-induced activation of Erk-1/2 was unaffected by transfection with dominant-negative N17 Ras but blocked by transfection with kinase-dead Raf-1. Consequently, LTD(4) regulates the proliferative response by a distinct Ras-independent, PKCepsilon-dependent activation of Erk-1/2 and a parallel Ras-dependent signaling pathway.

Increased Bcl-xL expression mediates v-Src-induced resistance to anoikis in intestinal epithelial cells

Acquisition of resistance to anoikis (detachment-induced apoptosis) is considered to be a requirement for transformed intestinal epithelial cells to invade surrounding tissues and metastasize to distant organs. Increased Src kinase activity, which is a feature of a large proportion of colorectal cancers, has been identified as one of the factors that can contribute to anoikis resistance. However, the molecular mechanism by which high levels of Src activity contribute to anoikis resistance in intestinal epithelial cells is unknown. Here we show that high Src activity confers resistance to anoikis in intestinal epithelial cells, at least in part, by inducing Bcl-xL overexpression, and that this induction is mediated by the MEK/MAPK pathway. Based on the findings reported here, and on our previous study showing that Bcl-xL plays a critical role in ras-induced resistance to anoikis, we propose that the increased Bcl-xL levels found in colorectal cancers play a significant role in the induction of resistance to anoikis during the progression of this disease.

FAK regulates tyrosine phosphorylation of CAS, paxillin, and PYK2 in cells expressing v-Src, but is not a critical determinant of v-Src transformation

FAK (focal adhesion kinase) is a nonreceptor protein-tyrosine kinase activated by tyrosine phosphorylation following integrin-mediated cell adhesion. Oncogenic Src promotes enhanced and deregulated FAK tyrosine phosphorylation which has been proposed to contribute to altered cell growth and/or morphological properties associated with transformation. In this study, an inducible FAK expression system was used to study the potential role of FAK in v-Src transformation. Our results portray FAK as a major v-Src substrate that also plays a role in recruiting v-Src to phosphorylate substrates CAS (Crk-associated substrate) and paxillin. The FAK Tyr-397 autophosphorylation site was necessary for this scaffolding function, but was not required for v-Src to stably interact with and phosphorylate FAK. FAK was also shown to negatively regulate v-Src mediated phosphorylation of the FAK-related kinase PYK2. Despite these effects, FAK does not play an essential role in targeting v-Src to major cellular substrates including CAS and paxillin. Nor is FAK strictly required to achieve the altered morphological and growth characteristics of v-Src transformed cells.

Functional cooperation among Ras, STAT5, and phosphatidylinositol 3-kinase is required for full oncogenic activities of BCR/ABL in K562 cells

BCR/ABL tyrosine kinase generated from the chromosomal translocation t(9;22) causes chronic myelogenous leukemia and acute lymphoblastic leukemia. To examine the roles of BCR/ABL-activated individual signaling molecules and their cooperation in leukemogenesis, we inducibly expressed a dominant negative (DN) form of Ras, phosphatidylinositol 3-kinase, and STAT5 alone or in combination in p210 BCR/ABL-positive K562 cells. The inducibly expressed DN Ras (N17), STAT5 (694F), and DN phosphatidylinositol 3-kinase (Delta p85) inhibited the growth by 90, 55, and 40%, respectively. During the growth inhibition, the expression of cyclin D2 and cyclin D3 was suppressed by N17, 694F, or Delta p85; that of cyclin E by N17; and that of cyclin A by Delta p85. In addition, N17 induced apoptosis in a small proportion of K562, whereas 694F and Delta p85 were hardly effective. In contrast, coexpression of two DN mutants in any combinations induced severe apoptosis. During these cultures, the expression of Bcl-2 was suppressed by N17, 694F, or Delta p85, and that of Bcl-XL by N17. Furthermore, although K562 was resistant to interferon-alpha- and dexamethasone-induced apoptosis, disruption of one pathway by N17, 694F, or Delta p85 sensitized K562 to these reagents. These results suggested that cooperation among these molecules is required for full leukemogenic activities of BCR/ABL.

p60(v-src) and serum control cell shape and apoptosis via distinct pathways in quail neuroretina cells

We made use of QNR cells transformed by a thermosensitive (tsNY68) strain of the Rous sarcoma virus (RSV) to compare the effect of p60(v-src) and serum in cultured nerve cells. In this system, both p60(v-src) heat inactivation and serum removal resulted in growth arrest in G1. In both cases, growth arrest was reversible since cell proliferation was rapidly re-induced following respectively p60v-src renaturation or serum re-addition. However, cells did not fully recover their ability to grow in soft agar, suggesting that, in contrast to the cell cycle machinery, the transforming capacities of these cells have been irreversibly altered. We found that p60(v-src) kinase activity prevented detachment from the substratum and cell death following serum removal. Thermal inactivation of p60(v-src) at restrictive temperature (41.5 degrees C), but not serum removal, resulted in dramatic morphological changes, which occurred 4 h after temperature shift up to 41.5 degrees C. Later on, typical features of apoptotic cells could be observed. Cell death was greatly reduced by the caspase-3 inhibitor ZVAD.FMK, but not by the caspase-1 inhibitor Ac-YVAD.CHO. Together, these results suggested that p60(v-src) and serum factors act on distinct pathways, at least in part. In an attempt to identify the signalling pathways involved in the cell response to p60(v-src) down regulation, we found that Erk and Rac were rapidly inactivated following temperature shift up to 41.5 degrees C. Thus, the combined effects of p60(v-src) and serum factors on the cytoskeleton dynamics and the apoptosis machinery are essential for full neoplastic transformation of neuroretina cells.

Downregulating PKC delta provides a PI3K/Akt-independent survival signal that overcomes apoptotic signals generated by c-Src overexpression

3Y1 rat fibroblasts overexpressing the tyrosine kinase c-Src (3Y1(c-Src) cells) become transformed by downregulation of protein kinase C delta (PKC delta). However, when 3Y1(c-Src) cells were subjected to serum withdrawal, they underwent apoptosis via a cytochrome c/caspase 9 pathway. In contrast, neither parental nor v-Src-transformed 3Y1 cells underwent apoptosis when subjected to serum withdrawal. If PKC delta was downregulated, the apoptotic phenotypes induced by serum withdrawal in the 3Y1(c-Src) cells were suppressed. The apparent survival signal generated by PKC delta downregulation was independent of the phosphatidylinositol-3-kinase (PI3K)/Akt survival pathway. Collectively, these data indicate that (1) c-Src overexpression renders cells sensitive to apoptotic stress, and (2) that downregulation of PKC delta provides a novel PI3K/Akt-independent survival signal capable of suppressing apoptotic signals.

Stat1-dependent and -independent pathways in IFN-gamma-dependent signaling

The paradigm that emerged from studies during the past decade established a central role for Jak-Stat (signal transducer and activator of transcription) signaling pathways in promoting the diverse cellular responses induced by interferon gamma (IFN-gamma). However, recent studies have shown that the IFN-gamma receptor activates additional signaling pathways and can regulate gene expression by Stat1-independent pathways. The diversity of gene-expression patterns mediated by Stat1-dependent and -independent mechanisms and the balance between these two pathways play an important role in the biological response to IFN-gamma.

Cytoplasmic death signal triggered by SRC-mediated phosphorylation of the adenovirus E4orf4 protein

In transformed cells, the adenovirus E4orf4 death factor works in part by inducing a Src-mediated cytoplasmic apoptotic signal leading to caspase-independent membrane blebbing and cell death. Here we show that Src-family kinases modulate E4orf4 phosphorylation on tyrosine residues. Mutation of tyrosines 26, 42, and 59 to phenylalanines inhibited Src-induced phosphorylation of E4orf4 in vivo and in vitro but had no effect on the molecular association of E4orf4 with Src. However, in contrast to wild-type E4orf4, the nonphosphorylatable E4orf4 mutant was unable to modulate Src-dependent phosphorylation and was deficient in recruiting a subset of tyrosine-phosphorylated proteins. Indeed, the Src substrates cortactin and p62dok were found to associate with wild-type E4orf4 but not with the nonphosphorylatable E4orf4. Importantly, the nonphosphorylatable mutant E4orf4 was preferentially distributed in the cell nucleus, was unable to induce membrane blebbing, and had a highly impaired killing activity. Conversely, an activated form of E4orf4 was obtained by mutation of tyrosine 42 to glutamic acid. This pseudophosphorylated mutant E4orf4 was enriched in the cytoplasm and plasma membrane, showed increased binding to phosphotyrosine-containing proteins, and induced a dramatic blebbing phenotype associated with increased cell death. Altogether, our findings strongly suggest that Src-mediated phosphorylation of adenovirus type 2 E4orf4 is critical to promoting its cytoplasmic and membrane localization and is required for the transduction of E4orf4-Src-dependent induction of membrane blebbing. We propose that E4orf4 acts in part by uncoupling Src-dependent signals to drive the formation of a signaling complex that triggers a cytoplasmic death signal.