Detection of functional PTEN lipid phosphatase protein and enzyme activity in squamous cell carcinomas of the head and neck, despite loss of heterozygosity at this locus

SOX2 in cancer stemness: tumor malignancy and therapeutic potentials

Cancer stem cells (CSCs), a minor subpopulation of tumor bulks with self-renewal and seeding capacity to generate new tumors, posit a significant challenge to develop effective and long-lasting anti-cancer therapies. The emergence of drug resistance appears upon failure of chemo-/radiation therapy to eradicate the CSCs, thereby leading to CSC-mediated clinical relapse. Accumulating evidence suggests that transcription factor SOX2, a master regulator of embryonic and induced pluripotent stem cells, drives cancer stemness, fuels tumor initiation, and contributes to tumor aggressiveness through major drug resistance mechanisms like epithelial-to-mesenchymal transition, ATP-binding cassette drug transporters, anti-apoptotic and/or pro-survival signaling, lineage plasticity, and evasion of immune surveillance. Gaining a better insight and comprehensive interrogation into the mechanistic basis of SOX2-mediated generation of CSCs and treatment failure might therefore lead to new therapeutic targets involving CSC-specific anti-cancer strategies.

SOX2 and squamous cancers

SOX2 is a pleiotropic nuclear transcription factor with major roles in stem cell biology and in development. Over the last 10 years SOX2 has also been implicated as a lineage-specific oncogene, notably in squamous carcinomas but also neurological tumours, particularly glioblastoma. Squamous carcinomas (SQCs) comprise a common group of malignancies for which there are no targeted therapeutic interventions. In this article we review the molecular epidemiological and laboratory evidence linking SOX2 with squamous carcinogenesis, explore in detail the multifaceted impact of SOX2 in SQC, describe areas of uncertainty and highlight areas for potential future research.

Loss of heterozygosity and immunoexpression of PTEN in oral epithelial dysplasia and squamous cell carcinoma

INTRODUCTION

Oral epithelial dysplasia (OED) is a risk factor for developing subsequent oral squamous cell carcinoma (OSCC). Loss of heterozygosity (LOH) profiles have been validated as risk predictors of malignant transformation of OED. It is still unclear if Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) allelic loss also occurs in initial stage malignant lesions and if the allelic loss is involved as one of the mechanisms of oral carcinogenesis. Thus, this study objective investigate LOH of PTEN gene and the immunohistochemical expression of the protein in OED and OSCC samples.

MATERIAL AND METHODS

Formalin-fixed paraffin-embedded samples of 19 OEDs and 16 OSCCs were included to immunohistochemistry and LOH analysis. Two polymorphic microsatellite markers (AFMA086WG9 and D10S1765) located in chromosome 10 were used in this study for LOH analysis. For immunohistochemical analysis, 5 random fields with 400× magnification were evaluated quantitatively and qualitatively in epithelial and neoplastic cells.

RESULTS

AFMA086WG9 marker only demonstrated LOH in OEDs cases (10.5%). D10S1765 marker demonstrated LOH in 57.2% of OEDs and 50% of OSCCs. Higher nuclear immunostaining was detected in cases of OSCCs when compared to OEDs (p < .001) and there was strong cytoplasmic immunoexpression in OSCCs (p < .045).

CONCLUSIONS

We provide evidence that the allelic loss of PTEN is present in premalignant oral lesions and OSCCs, however the LOH of PTEN does not seems to influence its protein expression.

Downregulation of miR-382 by propranolol inhibits the progression of infantile hemangioma via the PTEN-mediated AKT/mTOR pathway

Approximately 10% of infantile hemangiomas (IHs) are the most common vascular tumors affecting children and are characterized by rapid growth, and can have destructive, disfiguring and even life-threatening consequences. Currently, propranolol is considered to be a safe and effective treatment option for problematic proliferating IHs. Recent studies have also revealed that microRNAs (miRNAs or miRs) play important roles in the regulation of angiogenesis. In this study, XPTS‑1 cells were used as a hemangioma-derived endothelial cell line constructed in our laboratory. Through a series of experiments, we discovered that miR‑382 is a novel miRNA associated with IHs, which was overexpressed in XPTS‑1 cells and was conversely downregulated by treatment with propranolol. In addition, we found that miR‑382 contributes to the progression of IHs. Our results revealed that propranolol inhibited XPTS‑1 cell migration and proliferation, and promoted apoptosis, and these effects were reversed by the restoration of miR‑382 expression by transfection of the cells with an miR‑382 overexpression vector. Further experiments revealed that the above-mentioned effects were associated with the phosphatase and tensin homolog (PTEN)-mediated AKT/mammalian target of rapamycin (mTOR) signaling pathway. The expression of PTEN was upregulated, while that of p-AKT, p-mTOR and p-p70S6K was downregulated by propranolol; these effects were partly reversed by the overexpression of miR‑382. On the whole, our study identified that the downregulation of miR‑382 by propranolol inhibits the progression of IHs via the PTEN-mediated AKT/mTOR pathway.

Brassinin inhibits STAT3 signaling pathway through modulation of PIAS-3 and SOCS-3 expression and sensitizes human lung cancer xenograft in nude mice to paclitaxel

Persistent phosphorylation of signal transducers and activators of transcription 3 (STAT3) is frequently observed in tumor cells. We found that brassinin (BSN) suppressed both constitutive and IL-6-inducible STAT3 activation in lung cancer cells. Moreover, BSN induced PIAS-3 protein and mRNA, whereas the expression of SOCS-3 was reduced. Knockdown of PIAS-3 by small interfering RNA prevented inhibition of STAT3 and cytotoxicity by BSN. Overexpression of SOCS-3 in BSN-treated cells increased STAT3 phosphorylation and cell viability. BSN down-regulated STAT3-regulated gene products, inhibited proliferation, invasion, as well as induced apoptosis. Most importantly, when administered intraperitoneally, combination of BSN and paclitaxel significantly decreased the tumor development in a xenograft lung cancer mouse model associated with down-modulation of phospho-STAT3, Ki-67 and CD31. We suggest that BSN inhibits STAT3 signaling through modulation of PIAS-3 and SOCS-3, thereby attenuating tumor growth and increasing sensitivity to paclitaxel.

Senescence-Derived Extracellular Molecules as Modulators of Oral Cancer Development: A Mini-Review

Oral cancers are predominantly oral squamous cell carcinomas (OSCCs) derived from keratinocytes, and there is now very detailed knowledge of the genetics and molecular biology of the epithelial tumourigenic component of these cancers, including the identification of cancer stem or tumour-initiating cells. Several key genetic alterations have been identified including the near ubiquitous loss of the CDKN2A/p16INK4A and p53 pathways and telomerase activation, together with frequent inactivation of the NOTCH1 canonical pathway either by somatic genetic alterations or by the presence of human papilloma virus. There is also evidence that OSCCs arise from a ‘field' of altered cells and that malignant conversion takes place pre-dominantly at the microscopic level. However, in the last decade, it has been realised that tumour development and progression are influenced by the cells of the microenvironment with cross-talk between the epithelial (tumour) and mesenchymal components. OSCCs, especially those that have bypassed cellular senescence, produce an array of proteins and metabolites that induce cellular senescence in the normal surrounding cells; indeed, senescence is a common property of cancer-associated fibroblasts (CAFs). Cellular senescence is defined as an irreversible cell cycle arrest and is associated with the release of molecules known as the senescence-associated secretory phenotype that can selectively promote the growth of pre-neoplastic keratinocytes (osteopontin) and cancer invasion (transforming growth factor β, matrix metalloproteinases, interleukin 6 and lactate). In addition, both old and new work has shown that keratinocytes harbouring NOTCH loss-of-function mutations that lead to defective keratinocyte differentiation and loss of squamous epithelial barrier function may act as a tumour-promoting stimulus for initiated cells harbouring RAS pathway mutations by activating a wound response in the tumour mesenchyme. Thus, not all keratinocytes in the tumour tissue may be tumourigenic and may instead act as promoters of tumour growth and progression analogous to the much-studied CAFs which co-evolve with the genetically altered tumourigenic cells. This new data is discussed in relation to attempts to develop novel non-invasive diagnostics and therapeutics for oral cancer.

MicroRNA-382 induced by HIF-1α is an angiogenic miR targeting the tumor suppressor phosphatase and tensin homolog

Recent studies have revealed that microRNAs (miRs) play important roles in the regulation of angiogenesis. In this study, we have characterized miR-382 upregulation by hypoxia and the functional relevance of miR-382 in tumor angiogenesis. miRs induced by hypoxia in MKN1 human gastric cancer cells were investigated using miRNA microarrays. We selected miR-382 and found that the expression of miR-382 was regulated by HIF-1α. Conditioned media (CM) from MKN1 cells transfected with a miR-382 inhibitor (antagomiR-382) under hypoxic conditions significantly decreased vascular endothelial cell (EC) proliferation, migration and tube formation. Algorithmic programs (Target Scan, miRanda and cbio) predicted that phosphatase and tensin homolog (PTEN) is a target gene of miR-382. Deletion of miR382-binding sequences in the PTEN mRNA 3′-untranslated region (UTR) diminished the luciferase reporter activity. Subsequent study showed that the overexpression of miR-382 or antagomiR-382 down- or upregulated PTEN and its downstream target AKT/mTOR signaling pathway, indicating that PTEN is a functional target gene of miR-382. In addition, PTEN inhibited miR-382-induced in vitro and in vivo angiogenesis as well as VEGF secretion, and the inhibition of miR-382 expression reduced xenograft tumor growth and microvessel density in tumors. Taken together, these results suggest that miR-382 induced by hypoxia promotes angiogenesis and acts as an angiogenic oncogene by repressing PTEN.

The PRKCI and SOX2 oncogenes are coamplified and cooperate to activate Hedgehog signaling in lung squamous cell carcinoma

We report that two oncogenes coamplified on chromosome 3q26, PRKCI and SOX2, cooperate to drive a stem-like phenotype in lung squamous cell carcinoma (LSCC). Protein kinase Cι (PKCι) phosphorylates SOX2, a master transcriptional regulator of stemness, and recruits it to the promoter of Hedgehog (Hh) acyltransferase (HHAT) that catalyzes the rate-limiting step in Hh ligand production. PKCι-mediated SOX2 phosphorylation is required for HHAT promoter occupancy, HHAT expression, and maintenance of a stem-like phenotype. Primary LSCC tumors coordinately overexpress PKCι, SOX2, and HHAT and require PKCι-SOX2-HHAT signaling to maintain a stem-like phenotype. Thus, PKCι and SOX2 are genetically, biochemically, and functionally linked in LSCC, and together they drive tumorigenesis by establishing a cell-autonomous Hh signaling axis.

Regulation of axonal growth and neuromuscular junction formation by neuronal phosphatase and tensin homologue signaling

Axonal growth and synaptogenesis are sequential events of neuronal development. Phosphatase and tensin homologue (PTEN) is expressed in motor neurons, and its disruption leads to continued axonal extension, even upon muscle contact, leading to synaptogenic suppression. Thus PTEN is involved in target-mediated cessation of axonal growth and subsequent synaptic differentiation.

During the development of the vertebrate neuromuscular junction (NMJ), motor axon tips stop growing after contacting muscle and transform into presynaptic terminals that secrete the neurotransmitter acetylcholine and activate postsynaptic ACh receptors (AChRs) to trigger muscle contraction. The neuron-intrinsic signaling that retards axonal growth to facilitate stable nerve–muscle interaction and synaptogenesis is poorly understood. In this paper, we report a novel function of presynaptic signaling by phosphatase and tensin homologue (PTEN) in mediating a growth-to-synaptogenesis transition in neurons. In Xenopus nerve–muscle cocultures, axonal growth speed was halved after contact with muscle, when compared with before contact, but when cultures were exposed to the PTEN blocker bisperoxo (1,10-phenanthroline) oxovanadate, axons touching muscle grew ∼50% faster than their counterparts in control cultures. Suppression of neuronal PTEN expression using morpholinos or the forced expression of catalytically inactive PTEN in neurons also resulted in faster than normal axonal advance after contact with muscle cells. Significantly, interference with PTEN by each of these methods also led to reduced AChR clustering at innervation sites in muscle, indicating that disruption of neuronal PTEN signaling inhibited NMJ assembly. We thus propose that PTEN-dependent slowing of axonal growth enables the establishment of stable nerve–muscle contacts that develop into NMJs.

Insulin-like growth factor (IGF) binding protein 2 functions coordinately with receptor protein tyrosine phosphatase β and the IGF-I receptor to regulate IGF-I-stimulated signaling

Insulin-like growth factor I (IGF-I) is a mitogen for vascular smooth muscle cells (VSMC) and has been implicated in the development and progression of atherosclerosis. IGF binding proteins (IGFBPs) modify IGF-I actions independently of IGF binding, but a receptor-based mechanism by which they function has not been elucidated. We investigated the role of IGFBP-2 and receptor protein tyrosine phosphatase β (RPTPβ) in regulating IGF-I signaling and cellular proliferation. IGFBP-2 bound RPTPβ, which led to its dimerization and inactivation. This enhanced PTEN tyrosine phosphorylation and inhibited PTEN activity. Utilization of substrate trapping and phosphatase-dead mutants showed that RPTPβ bound specifically to PTEN and dephosphorylated it. IGFBP-2 knockdown led to decreased PTEN tyrosine phosphorylation and decreased AKT Ser473 activation. IGFBP-2 enhanced IGF-I-stimulated VSMC migration and proliferation. Analysis of aortas obtained from IGFBP-2(-/-) mice showed that RPTPβ was activated, and this was associated with inhibition of IGF-I stimulated AKT Ser473 phosphorylation and VSMC proliferation. These changes were rescued following administration of IGFBP-2. These findings present a novel mechanism for coordinate regulation of IGFBP-2 and IGF-I signaling functions that lead to stimulation of VSMC proliferation. The results have important implications for understanding how IGFBPs modulate the cellular response to IGF-I.

PTEN-mediated AKT activation contributes to the reduced apoptosis among Indian oral squamous cell carcinoma patients

PURPOSE

The tumor suppressor gene PTEN negatively regulates Akt, a downstream mediator phosphoinositol 3-kinase. Several studies have reported the role of PTEN gene in Akt downregulation and apoptosis induction in different cancers and cell lines. However, the role of loss of PTEN expression in Akt activation and spontaneous apoptosis in oral squamous cell carcinoma clinical specimens is not well established.

METHODS

We investigated the expression of PTEN and phospho-Akt in 146 formalin-fixed (archived) paraffin-embedded oral squamous cell carcinoma tissue sections through immunohistochemical analysis. Programmed cell death (apoptosis) was determined by Terminal deoxynucleotidyl Transferase Biotin-dUTP Nick End Labeling assay.

RESULTS

Sixty-one percent loss of PTEN expression and 68.5% Akt activation was observed in oral squamous cell carcinoma. A significant correlation was found between loss of PTEN expression and Akt activation. Loss of PTEN expression and Akt activation were further correlated with different clinical parameters and found to be significantly correlated with tumor stage. Apoptotic index was estimated and correlated with PTEN expression and Akt activation. The percentage of apoptotic cells varied from 0.2 to 14.1%. Low apoptotic index was observed in 105 (72%) of samples, and it was found to be significantly related with loss of PTEN expression and phospho-Akt

CONCLUSION

The present study confirms the contribution of loss of PTEN expression in Akt phosphorylation and spontaneous apoptosis suppression in the specimens of oral cancer. Both PTEN and phospho-Akt are likely to be concerned with oral cancer progression and reduced incidence of spontaneous apoptosis.

Protein kinase Cι expression and oncogenic signaling mechanisms in cancer

Accumulating evidence demonstrates that PKCι is an oncogene and prognostic marker that is frequently targeted for genetic alteration in many major forms of human cancer. Functional data demonstrate that PKCι is required for the transformed phenotype of lung, pancreatic, ovarian, prostate, colon, and brain cancer cells. Future studies will be required to determine whether PKCι is also an oncogene in the many other cancer types that also overexpress PKCι. Studies of PKCι using genetically defined models of tumorigenesis have revealed a critical role for PKCι in multiple stages of tumorigenesis, including tumor initiation, progression, and metastasis. Recent studies in a genetic model of lung adenocarcinoma suggest a role for PKCι in transformation of lung cancer stem cells. These studies have important implications for the therapeutic use of aurothiomalate (ATM), a highly selective PKCι signaling inhibitor currently undergoing clinical evaluation. Significant progress has been made in determining the molecular mechanisms by which PKCι drives the transformed phenotype, particularly the central role played by the oncogenic PKCι-Par6 complex in transformed growth and invasion, and of several PKCι-dependent survival pathways in chemo-resistance. Future studies will be required to determine the composition and dynamics of the PKCι-Par6 complex, and the mechanisms by which oncogenic signaling through this complex is regulated. Likewise, a better understanding of the critical downstream effectors of PKCι in various human tumor types holds promise for identifying novel prognostic and surrogate markers of oncogenic PKCι activity that may be clinically useful in ongoing clinical trials of ATM.

Inhibition of Epidermal Growth Factor Receptor and PI3K/Akt Signaling Suppresses Cell Proliferation and Survival through Regulation of Stat3 Activation in Human Cutaneous Squamous Cell Carcinoma

Recent studies have emphasized the important role of Stat3 activation in a number of human tumors from the viewpoint of its oncogenic and antiapoptotic activity. In this study, we examined the role and related signaling molecules of Stat3 in the carcinogenesis of human cutaneous squamous cell carcinoma (SCC). In 35 human cutaneous SCC samples, 86% showed overexpression of phosphorylated (p)-Stat3, and most of those simultaneously overexpressed p-EGFR or p-Akt. Constitutive activation of EGFR and Stat3 was observed in three SCC cell lines and four of five SCC tissues. AG1478, an inhibitor of the EGFR, downregulated Stat3 activation in HSC-1 human SCC cells. AG1478 inhibited cell proliferation and induced apoptosis of HSC-1 cells but did not inhibit the growth of normal human epidermal keratinocytes that did not show Stat3 activation. Furthermore, a PI3K inhibitor also suppressed Stat3 activation in HSC-1 cells to some degree. Combined treatment with the PI3K inhibitor and AG1478 strongly suppressed Stat3 activity and dramatically induced apoptosis of HSC-1 cells. These data suggest that Stat3 activation through EGFR and/or PI3K/Akt activation plays a critical role in the proliferation and survival of human cutaneous SCC.

Ect2 links the PKCiota-Par6alpha complex to Rac1 activation and cellular transformation

Protein kinase Ciota (PKCiota) promotes non-small cell lung cancer (NSCLC) by binding to Par6alpha and activating a Rac1-Pak-Mek1,2-Erk1,2 signaling cascade. The mechanism by which the PKCiota-Par6alpha complex regulates Rac1 is unknown. Here we show that epithelial cell transforming sequence 2 (Ect2), a guanine nucleotide exchange factor for Rho family GTPases, is coordinately amplified and overexpressed with PKCiota in NSCLC tumors. RNA interference-mediated knockdown of Ect2 inhibits Rac1 activity and blocks transformed growth, invasion and tumorigenicity of NSCLC cells. Expression of constitutively active Rac1 (RacV12) restores transformation to Ect2-deficient cells. Interestingly, the role of Ect2 in transformation is distinct from its well-established role in cytokinesis. In NSCLC cells, Ect2 is mislocalized to the cytoplasm where it binds the PKCiota-Par6alpha complex. RNA interference-mediated knockdown of either PKCiota or Par6alpha causes Ect2 to redistribute to the nucleus, indicating that the PKCiota-Par6alpha complex regulates the cytoplasmic localization of Ect2. Our data indicate that Ect2 and PKCiota are genetically and functionally linked in NSCLC, acting to coordinately drive tumor cell proliferation and invasion through formation of an oncogenic PKCiota-Par6alpha-Ect2 complex.

MicroRNA-184 antagonizes microRNA-205 to maintain SHIP2 levels in epithelia

Despite their potential to regulate approximately one-third of the whole genome, relatively few microRNA (miRNA) targets have been experimentally validated, particularly in stratified squamous epithelia. Here we demonstrate not only that the lipid phosphatase SHIP2 is a target of miRNA-205 (miR-205) in epithelial cells, but, more importantly, that the corneal epithelial-specific miR-184 can interfere with the ability of miR-205 to suppress SHIP2 levels. This is the first example of a miRNA negatively regulating another to maintain levels of a target protein. Interfering with miR-205 function by using a synthetic antagomir, or by the ectopic expression of miR-184, leads to a coordinated damping of the Akt signaling pathway via SHIP2 induction. This was associated with a marked increase in keratinocyte apoptosis and cell death. Aggressive squamous cell carcinoma (SCC) cells exhibited elevated levels of miR-205. This was associated with a concomitant reduction in SHIP2 levels. Partial knockdown of endogenous miR-205 in SCCs markedly decreased phosphorylated Akt and phosphorylated BAD levels and increased apoptosis. We were able to increase SHIP2 levels in SCC cells after inhibition of miR-205. Therefore, miR-205 might have diagnostic value in determining the aggressivity of SCCs. Blockage of miR-205 activity with an antagomir or via ectopic expression of miR-184 could be novel therapeutic approaches for treating aggressive SCCs.

Atypical protein kinase C iota expression and aurothiomalate sensitivity in human lung cancer cells

The antirheumatoid agent aurothiomalate (ATM) is a potent inhibitor of oncogenic PKC iota. ATM inhibits non-small lung cancer (NSCLC) growth by binding PKC iota and blocking activation of a PKC iota-Par6-Rac1-Pak-Mek 1,2-Erk 1,2 signaling pathway. Here, we assessed the growth inhibitory activity of ATM in a panel of human cell lines representing major lung cancer subtypes. ATM inhibited anchorage-independent growth in all lines tested with IC(50)s ranging from approximately 300 nmol/L to >100 micromol/L. ATM sensitivity correlates positively with expression of PKC iota and Par6, but not with the PKC iota binding protein p62, or the proposed targets of ATM in rheumatoid arthritis (RA), thioredoxin reductase 1 or 2. PKC iota expression profiling revealed that a significant subset of primary NSCLC tumors express PKC iota at or above the level associated with ATM sensitivity. ATM sensitivity is not associated with general sensitivity to the cytotoxic agents cis-platin, placitaxel, and gemcitabine. ATM inhibits tumorigenicity of both sensitive and insensitive lung cell tumors in vivo at plasma drug concentrations achieved in RA patients undergoing ATM therapy. ATM inhibits Mek/Erk signaling and decreases proliferative index without effecting tumor apoptosis or vascularization in vivo. We conclude that ATM exhibits potent antitumor activity against major lung cancer subtypes, particularly tumor cells that express high levels of the ATM target PKC iota and Par6. Our results indicate that PKC iota expression profiling will be useful in identifying lung cancer patients most likely to respond to ATM therapy in an ongoing clinical trial.

Matrix metalloproteinase-10 is a critical effector of protein kinase Ciota-Par6alpha-mediated lung cancer

Protein kinase Ciota (PKCiota) drives transformed growth of non-small cell lung cancer (NSCLC) cells through the Rho family GTPase Rac1. We show here that PKCiota activates Rac1 in NSCLC cells by formation of a PKCiota-Par6alpha complex that drives anchorage-independent growth and invasion through activation of matrix metalloproteinase-10 (MMP-10) expression. RNAi-mediated knockdown of PKCiota, Par6alpha or Rac1 expression inhibits NSCLC transformation and MMP-10 expression in vitro. Expression of wild-type Par6alpha in Par6alpha-deficient cells restores transformation and MMP-10 expression, whereas expression of Par6alpha mutants that either cannot bind PKCiota (Par6alpha-K19A) or couple to Rac1 (Par6alpha-DeltaCRIB) do not. Knockdown of MMP-10 expression blocks anchorage-independent growth and invasion of NSCLC cells and addition of catalytically active MMP-10 to PKCiota- or Par6alpha-deficient cells restores anchorage-independent growth and invasion. Dominant-negative PKCiota inhibits tumorigenicity and MMP-10 expression in subcutaneous NSCLC tumors. MMP-10 and PKCiota are coordinately overexpressed in primary NSCLC tumors, and tumor MMP-10 expression predicts poor survival in NSCLC patients. Our data define a PKCiota-Par6alpha-Rac1 signaling axis that drives anchorage-independent growth and invasion of NSCLC cells through induction of MMP-10 expression.

Targeting the oncogenic protein kinase Ciota signalling pathway for the treatment of cancer

PKC (protein kinase C) isoenzymes are key signalling components involved in the regulation of normal cell proliferation, differentiation, polarity and survival. The aberrant regulation of PKC isoenzymes has been implicated in the development of many human diseases including cancer [Fields and Gustafson (2003) Methods Mol. Biol. 233, 519-537]. To date, however, only one PKC isoenzyme, the aPKC [atypical PKCiota (protein kinase Ciota)], has been identified as a human oncogene [Regala, Weems, Jamieson, Khoor, Edell, Lohse and Fields (2005) Cancer Res. 65, 8905-8911]. PKCiota has also proven to be a useful prognostic marker and legitimate target for the development of novel pharmacological agents for the treatment of cancer. The PKCiota gene resides at chromosome 3q26 and is a frequent target of tumour-specific gene amplification in multiple forms of human cancer. PKCiota gene amplification in turn drives PKCiota overexpression in these cancers. Genetic disruption of PKCiota expression blocks multiple aspects of the transformed phenotype of human cancer cells including transformed growth in soft agar, invasion through Matrigel and growth of subcutaneous tumours in nude mice. Genetic dissection of oncogenic PKCiota signalling mechanisms demonstrates that PKCiota drives transformed growth by activating a PKCiota --> Rac1 --> PAK (p21-activated kinase) --> MEK [MAPK (mitogen-activated protein kinase) 1,2/ERK (extracellular-signal-regulated kinase) kinase] 1,2 signalling pathway [Regala, Weems, Jamieson, Copland, Thompson and Fields (2005) J. Biol. Chem. 280, 31109-31115]. The transforming activity of PKCiota requires the N-terminal PB1 (Phox-Bem1) domain of PKCiota, which serves to couple PKCiota with downstream effector molecules. Hence, there exists a strong rationale for developing novel cancer therapeutics that target the PB1 domain of PKCiota and thereby disrupt its interactions with effector molecules. Using a novel high-throughput drug screen, we identified compounds that can disrupt PB1-PB1 domain interactions between PKCiota and the adaptor molecule Par6 [Stallings-Mann, Jamieson, Regala, Weems, Murray and Fields (2006) Cancer Res. 66, 1767-1774]. Our screen identified the gold compounds ATG (aurothioglucose) and ATM (aurothiomalate) as specific inhibitors of the PB1-PB1 domain interaction between PKCiota and Par6 that exhibit anti-tumour activity against NSCLC (non-small-cell lung cancer) both in vitro and in vivo. Structural analysis, site-directed mutagenesis and modelling indicate that ATM specifically targets the PB1 domain of PKCiota to mediate its anti-tumour activity [Erdogan, Lamark, Stallings-Mann, Lee, Pellechia, Thompson, Johansen and Fields (2006) J. Biol. Chem. 281, 28450-28459]. Taken together, our recent work demonstrates that PKCiota signalling is required for transformed growth of human tumours and is an attractive target for development of mechanism-based cancer therapies. ATM is currently in Phase I clinical trials for the treatment of NSCLC.

3q26 Amplification and polysomy of chromosome 3 in squamous cell lesions of the lung: a fluorescence in situ hybridization study

PURPOSE

An overlapping area of gain at 3q26 has been reported in lung squamous cell carcinoma (SCC), but whether this also occurs in preneoplastic/preinvasive squamous cell proliferations and early-stage invasive carcinomas of the lung is still unknown.

EXPERIMENTAL DESIGN

We evaluated the prevalence and the clinicopathologic implications of 3q26 amplification and polysomy of chromosome 3 in 31 preneoplastic/preinvasive squamous cell lesions of the bronchial mucosa and in 139 early-stage invasive pulmonary SCC, both of limited growth within the bronchial wall [early hilar SCC (EHSCC)] and involving the pulmonary parenchyma [parenchyma-infiltrating SCC (PISCC)]. Moreover, mRNA expression of two candidate genes (h-TERC and SKI-like), both mapping to the minimal common amplification region, was also studied by quantitative real-time reverse transcription-PCR.

RESULTS

3q26 amplification and polysomy of chromosome 3 were confined to malignant samples, with 37% of invasive SCC, and 27% of severe dysplasias/in situ carcinomas showing these chromosomal abnormalities. Amplification (with minimal common amplification region at 3q26.2), polysomy 3, concurrent amplification and polysomy 3, or other changes (monosomy) were found in 25 SCC and 1 dysplasia, 24 and 2, 2 and 0, and 1 and 0, respectively. Amplification was significantly associated with EHSCC, polysomy 3 with PISCC. 3q26 amplification correlated with increased tumor diameter and a history of smoking, whereas polysomy 3 correlated with tumor diameter, pT class, and p53, p21, and fascin immunoreactivity. No relationship of either 3q26 gain or polysomy was found with patients' survival. Overexpression of h-TERC or SKI-like mRNA was found in 3q26-amplified or polysomic SCC, with higher levels of h-TERC in the former and of SKI-like in the latter.

CONCLUSIONS

3q26 amplification and chromosome 3 polysomy may be related to the development of invasive SCC, with differential distribution in tumor subsets, despite substantial histologic uniformity. Both h-TERC and SKI-like may be involved in tumor progression.

Protein kinase C iota: human oncogene, prognostic marker and therapeutic target

The protein kinase C (PKC) family of serine/threonine kinases has been the subject of intensive study in the field of cancer since their initial discovery as major cellular receptors for the tumor promoting phorbol esters nearly 30 years ago. However, despite these efforts, the search for a direct genetic link between members of the PKC family and human cancer has yielded only circumstantial evidence that any PKC isozyme is a true cancer gene. This situation changed in the past year with the discovery that atypical protein kinase C iota (PKC iota) is a bonafide human oncogene. PKC iota is required for the transformed growth of human cancer cells and the PKC iota gene is the target of tumor-specific gene amplification in multiple forms of human cancer. PKC iota participates in multiple aspects of the transformed phenotype of human cancer cells including transformed growth, invasion and survival. Herein, we review pertinent aspects of atypical PKC structure, function and regulation that relate to the role of these enzymes in oncogenesis. We discuss the evidence that PKC iota is a human oncogene, review mechanisms controlling PKC iota expression in human cancers, and describe the molecular details of PKC iota-mediated oncogenic signaling. We conclude with a discussion of how oncogenic PKC iota signaling has been successfully targeted to identify a novel, mechanism-based therapeutic drug currently entering clinical trials for treatment of human lung cancer. Throughout, we identify key unanswered questions and exciting future avenues of investigation regarding this important oncogenic molecule.

Atypical protein kinase C iota is an oncogene in human non-small cell lung cancer

Protein kinase C (PKC) isozymes have long been implicated in carcinogenesis. However, little is known about the functional significance of these enzymes in human cancer. We recently showed that the atypical PKC (aPKC) isozyme PKCiota is overexpressed in human non-small cell lung cancer (NSCLC) cells and that PKCiota plays a critical role in the transformed growth of the human lung adenocarcinoma A549 cell line in vitro and tumorigenicity in vivo. Here we provide compelling evidence that PKCiota is an oncogene in NSCLC based on the following criteria: (a) aPKCiota is overexpressed in the vast majority of primary NSCLC tumors; (b) tumor PKCiota expression levels predict poor survival in patients with NSCLC; (c) the PKCiota gene is frequently amplified in established NSCLC cell lines and primary NSCLC tumors; (d) gene amplification drives PKCiota expression in NSCLC cell lines and primary NSCLC tumors; and (e) disruption of PKCiota signaling with a dominant negative PKCiota allele blocks the transformed growth of human NSCLC cells harboring PKCiota gene amplification. Taken together, our data provide conclusive evidence that PKCiota is required for the transformed growth of NSCLC cells and that the PKCiota gene is a target for tumor-specific genetic alteration by amplification. Interestingly, PKCiota expression predicts poor survival in NSCLC patients independent of tumor stage. Therefore, PKCiota expression profiling may be useful in identifying early-stage NSCLC patients at elevated risk of relapse. Our functional data indicate that PKCiota is an attractive target for development of novel, mechanism-based therapeutics to treat NSCLC.

PTEN expression in non-small-cell lung cancer: evaluating its relation to tumor characteristics, allelic loss, and epigenetic alteration

The tumor suppressor PTEN encodes a lipid phosphatase that negatively regulates the phosphatidylinositol 3-kinase/AKT cell survival pathway. Mutations of this gene are common in brain, prostate, endometrial, and gastric cancers but occur rarely in non-small-cell lung cancer (NSCLC), although the PTEN protein is often lost in lung tumors. We have studied hypermethylation of the PTEN promoter, loss of heterozygosity (LOH) at microsatellites in chromosome 10q23 (surrounding and intragenic to the PTEN locus), and hypermethylation of PTEN's highly homologous pseudogene, PTENP1, and their association with PTEN protein loss in a surgical case series study of primary NSCLC. PTEN protein expression was reduced or lost in 74% (86/117) of tumors, with loss occurring more often in well to moderately differentiated tumors. In squamous cell carcinomas, PTEN loss occurred significantly more often in early-stage (stage I or II) disease. PTEN protein loss also occurred more frequently in tumors with low to no aberrant TP53 staining. Methylation of PTEN occurred in 26% (39/151) of tumors, and LOH at 10q23 was rare, occurring in only 19% (17/90) of informative tumors. Neither methylation nor LOH was a significant predictor of PTEN protein expression, although LOH occurred exclusively in early-stage disease. In NSCLC, loss of PTEN protein expression occurs frequently, although the mechanism responsible for loss is not clearly attributable to deletion or epigenetic silencing. PTEN loss may also be a favorable prognostic marker, although further studies are needed to confirm this finding.

Frequent genetic and biochemical alterations of the PI 3-K/AKT/PTEN pathway in head and neck squamous cell carcinoma

We investigated the status of the PI 3-kinase/AKT/PTEN signaling pathway in a series of 117 head and neck squamous cell carcinomas (HNSCC) in a search for molecular alterations in genes/proteins with potential prognostic value. For this purpose, PIK3CA and AKT2 gene amplification was assessed by multiplex and Quantitative Real-Time PCR. Protein expression of AKT, p-AKT, p110alpha and PTEN was determined by Western blot. PTEN allelic loss was evaluated by microsatellite analysis. PTEN-exon 5 was screened for point mutations by PCR-SSCP. Homozygous deletions were determined by multiplex PCR. PIK3CA gene was amplified in 43/117 (37%) fresh tumor samples, a frequency that did not differ from that found in archival premalignant tissues: 15/38 (39%); 12/40 (30%) fresh tumors harbored AKT2 gene amplification. AKT was found activated in 6/36 (17%) fresh tumor samples, when compared to their normal tissue counterparts. Of these 6 cases, 1 showed p110alpha overexpression and 5 displayed PTEN protein downregulation. Neither allelic loss (found in 11/77 informative cases) nor point mutations or homozygous deletions accounted for the reduced PTEN protein expression observed in our tumor series. The histologically normal mucosa of 4 patients displayed some of the molecular alterations analyzed. Dysregulation of the PI 3-K/AKT/PTEN pathway might contribute to early HNSCC tumorigenesis and might constitute a potential clinical target. Overall, 17/36 (47%) cases showed at least 1 of the molecular alterations studied here, which makes the PI 3-kinase-initiated signaling pathway one of the most frequently altered in HNSCC.

Loss of heterozygosity as a predictor to map tumor suppressor genes in cancer: molecular basis of its occurrence

High frequency of chromosomal deletions elicited as losses of heterozygosity is a hallmark of genomic instability in cancer. Functional losses of tumor suppressor genes caused by loss of heterozygosity at defined regions during clonal selection for growth advantage define the minimally lost regions as their likely locations on chromosomes. Loss of heterozygosity is elicited at the molecular or cytogenetic level as a deletion, a gene conversion, single or double homologous and nonhomologous mitotic recombinations, a translocation, chromosome breakage and loss, chromosomal fusion or telomeric end-to-end fusions, or whole chromosome loss with or without accompanying duplication of the retained chromosome. Because of the high level of specificity, loss of heterozygosity has recently become invaluable as a marker for diagnosis and prognosis of cancer. The molecular defects for the occurrence of loss of heterozygosity are derived from disabled caretaker genes, which protect the integrity of DNA, or chromosome segregator genes, which mediate faithful chromosome disjunction.