Protein kinase C iota as a therapeutic target in alveolar rhabdomyosarcoma

Prkci promotes colorectal cancer metastasis by phosphorylating and stabilizing Tgfbr1 to activate TGF-β signaling

Colorectal cancer is one of the most common malignancies worldwide, with metastasis being the leading cause of cancer-related mortality. However, the molecular mechanisms driving CRC metastasis remain poorly understood. In this study, we identified Prkci as a critical oncogenic driver in CRC metastasis. Prkci was significantly upregulated in metastatic CRC tissues. Mechanistically, Prkci phosphorylated and stabilized Tgfbr1, a key receptor in the Transforming Growth Factor Beta signaling pathway, preventing its proteasomal degradation and amplifying downstream signaling cascades. This stabilization promoted epithelial-to-mesenchymal transition, enhancing migratory and invasive capacities of CRC cells. In vivo, Prkci knockout significantly reduced liver and lung metastases and prolonged survival in mouse models, highlighting its therapeutic potential. These findings establish Prkci as a promising therapeutic target for suppressing CRC metastasis and improving outcomes for metastatic CRC patients.

Taxane-Associated Acute Pain Syndrome: a Review of its Features and Management

OPINION STATEMENT

Taxane-associated acute pain syndrome (T-APS) is one of the most common adverse effects of taxane treatment and significantly reduces the quality of life and activities of daily living of patients. T-APS is recognized as myalgia and arthralgia, which generally appear 1-3 days after taxane administration and last for approximately 7 days, at a wide range of sites. Recently, T-APS has been suggested to be not only an acute symptom but also a chronic symptom associated with chemotherapy-induced peripheral neuropathy (CIPN). The reported incidence of T-APS varies among studies, possibly owing to differences in observation points, evaluation methods, taxane administration methods, concomitant medications, or patient factors. Several factors, such as high taxane dose, paclitaxel use, metastatic setting, breast cancer, younger age, and co-administration of pegfilgrastim, are associated with symptom development. Several findings regarding T-APS management, such as prophylaxis using corticosteroids, Shakuyaku-Kanzo-to, and non-steroidal anti-inflammatory drugs (NSAIDs), are present. Corticosteroids for several days after taxane administration dose-dependently prevents and attenuates T-APS although we should be cautious about its longer administration. Prophylactic administration of Shakuyaku-Kanzo-to, a herbal compound, may be useful, although prescriptions are only available in limited areas. Etoricoxib, a selective cyclooxygenase-2 inhibiting NSAID, also reduces the incidence and severity of T-APS. Additionally, its prophylactic administration decreases CIPN. In contrast, evidence of symptomatic medication is limited. Taxanes are key chemotherapeutic agents used in the treatment of several types of cancer; therefore, further assessment of mechanisms of action and treatment of T-APS is necessary.

MicroRNAs as the critical regulators of autophagy-mediated cisplatin response in tumor cells

Chemotherapy is one of the most common therapeutic methods in advanced and metastatic tumors. Cisplatin (CDDP) is considered as one of the main first-line chemotherapy drugs in solid tumors. However, there is a high rate of CDDP resistance in cancer patients. Multi-drug resistance (MDR) as one of the main therapeutic challenges in cancer patients is associated with various cellular processes such as drug efflux, DNA repair, and autophagy. Autophagy is a cellular mechanism that protects the tumor cells toward the chemotherapeutic drugs. Therefore, autophagy regulatory factors can increase or decrease the chemotherapy response in tumor cells. MicroRNAs (miRNAs) have a pivotal role in regulation of autophagy in normal and tumor cells. Therefore, in the present review, we discussed the role of miRNAs in CDDP response through the regulation of autophagy. It has been reported that miRNAs mainly increased the CDDP sensitivity in tumor cells by inhibition of autophagy. PI3K/AKT signaling pathway and autophagy-related genes (ATGs) were the main targets of miRNAs in the regulation of autophagy-mediated CDDP response in tumor cells. This review can be an effective step to introduce the miRNAs as efficient therapeutic options to increase autophagy-mediated CDDP sensitivity in tumor cells.

CircRNAs: Roles in regulating head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC), the most common head and neck malignant tumor, with only monotherapy, is characterized by poor prognosis, and low 5-year survival rate. Due to the lack of therapeutic targets, the targeted drugs for HNSCC are rare. Therefore, exploring the regulation mechanism of HNSCC and identifying effective therapeutic targets will be beneficial to its treatment of. Circular RNA (CircRNA) is a class of RNA molecules with a circular structure, which is widely expressed in human body. CircRNAs regulate gene expression by exerting the function as a miRNA sponge, thereby mediating the occurrence and development of HNSCC cell proliferation, apoptosis, migration, invasion, and other processes. In addition, circRNAs are also involved in the regulation of tumor sensitivity to chemical drugs and other biological functions. In this review, we systematically listed the functions of circRNAs and explored the regulatory mechanisms of circRNAs in HNSCC from the aspects of tumor growth, cell death, angiogenesis, tumor invasion and metastasis, tumor stem cell regulation, tumor drug resistance, immune escape, and tumor microenvironment. It will assist us in discovering new diagnostic markers and therapeutic targets, while encourage new ideas for the diagnosis and treatment of HNSCC.

Evaluating the current status of protein kinase C (PKC)-protein kinase D (PKD) signalling axis as a novel therapeutic target in ovarian cancer

Ovarian cancer, especially high grade serous ovarian cancer is one of the most lethal gynaecological malignancies with high relapse rate and patient death. Notwithstanding development of several targeted treatment and immunotherapeutic approaches, researchers fail to turn ovarian cancer into a manageable disease. Protein kinase C (PKC) and protein kinase D (PKD) are families of evolutionarily conserved serine/threonine kinases that can be activated by a plethora of extracellular stimuli such as hormones, growth factors and G-protein coupled receptor agonists. Recent literature suggests that a signalling cascade initiated by these two protein kinases regulates a battery of cellular and physiological processes involved in tumorigenesis including cell proliferation, migration, invasion and angiogenesis. In an urgent need to discover novel therapeutic interventions against a deadly pathology like ovarian cancer, we have discussed the status quo of PKC/PKD signalling axis in context of this disease. Additionally, apart from discussing the structural properties and activation mechanisms of PKC/PKD, we have provided a comprehensive review of the recent reports on tumor promoting functions of PKC isoforms and discussed the potential of PKC/PKD signalling axis as a novel target in this lethal pathology. Furthermore, in this review, we have discussed the significance of several recent clinical trials and development of small molecule inhibitors that target PKC/PKD signalling axis in ovarian cancer.

circPARD3 drives malignant progression and chemoresistance of laryngeal squamous cell carcinoma by inhibiting autophagy through the PRKCI-Akt-mTOR pathway

Background

Laryngeal squamous cell carcinoma (LSCC) is the second most common malignant tumor in head and neck. Autophagy and circular RNAs (circRNAs) play critical roles in cancer progression and chemoresistance. However, the function and mechanism of circRNA in autophagy regulation of LSCC remain unclear.

Methods

The autophagy-suppressive circRNA circPARD3 was identified via RNA sequencing of 107 LSCC tissues and paired adjacent normal mucosal (ANM) tissues and high-content screening. RT-PCR, Sanger sequencing, qPCR and fluorescence in situ hybridization were performed to detect circPARD3 expression and subcellular localization. Biological functions of circPARD3 were assessed by proliferation, migration, invasion, autophagic flux, and chemoresistance assays using in vitro and in vivo models. The mechanism of circPARD3 was investigated by RNA immunoprecipitation, RNA pulldown, luciferase reporter assays, western blotting and immunohistochemical staining.

Results

Autophagy was inhibited in LSCC, and circPARD3 was upregulated in the LSCC tissues (n = 100, p < 0.001). High circPARD3 level was associated with advanced T stages (p < 0.05), N stages (p = 0.001), clinical stages (p < 0.001), poor differentiation degree (p = 0.025), and poor prognosis (p = 0.002) of LSCC patients (n = 100). Functionally, circPARD3 inhibited autophagy and promoted LSCC cell proliferation, migration, invasion and chemoresistance. We further revealed that activation of the PRKCI-Akt-mTOR pathway through sponging miR-145-5p was the main mechanism of circPARD3 inhibited autophagy, promoting LSCC progression and chemoresistance.

Conclusion

Our study reveals that the novel autophagy-suppressive circPARD3 promotes LSCC progression and chemoresistance through the PRKCI-Akt-mTOR pathway, providing new insights into circRNA-mediated autophagy regulation and potential biomarker and target for LSCC treatment.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-020-01279-2.

Chemoradiation impairs myofiber hypertrophic growth in a pediatric tumor model

Pediatric cancer treatment often involves chemotherapy and radiation, where off-target effects can include skeletal muscle decline. The effect of such treatments on juvenile skeletal muscle growth has yet to be investigated. We employed a small animal irradiator to administer fractionated hindlimb irradiation to juvenile mice bearing implanted rhabdomyosarcoma (RMS) tumors. Hindlimb-targeted irradiation (3 × 8.2 Gy) of 4-week-old mice successfully eliminated RMS tumors implanted one week prior. After establishment of this preclinical model, a cohort of tumor-bearing mice were injected with the chemotherapeutic drug, vincristine, alone or in combination with fractionated irradiation (5 × 4.8 Gy). Single myofiber analysis of fast-contracting extensor digitorum longus (EDL) and slow-contracting soleus (SOL) muscles was conducted 3 weeks post-treatment. Although a reduction in myofiber size was apparent, EDL and SOL myonuclear number were differentially affected by juvenile irradiation and/or vincristine treatment. In contrast, a decrease in myonuclear domain (myofiber volume/myonucleus) was observed regardless of muscle or treatment. Thus, inhibition of myofiber hypertrophic growth is a consistent feature of pediatric cancer treatment.

Measuring the lactate-to-creatine ratio via 1H NMR spectroscopy can be used to noninvasively evaluate apoptosis in glioma cells after X-ray irradiation

BACKGROUND

Radiotherapy is among the commonly applied treatment options for glioma, which is one of the most common types of primary brain tumor. To evaluate the effect of radiotherapy noninvasively, it is vital for oncologists to monitor the effects of X-ray irradiation on glioma cells. Preliminary research had showed that PKC-ι expression correlates with tumor cell apoptosis induced by X-ray irradiation. It is also believed that the lactate-to-creatine (Lac/Cr) ratio can be used as a biomarker to evaluate apoptosis in glioma cells after X-ray irradiation. In this study, we evaluated the relationships between the Lac/Cr ratio, apoptotic rate, and protein kinase C iota (PKC-ι) expression in glioma cells.

METHODS

Cells of the glioma cell lines C6 and U251 were randomly divided into 4 groups, with every group exposed to X-ray irradiation at 0, 1, 5, 10 and 15 Gy. Single cell gel electrophoresis (SCGE) was conducted to evaluate the DNA damage. Flow cytometry was performed to measure the cell cycle blockage and apoptotic rates. Western blot analysis was used to detect the phosphorylated PKC-ι (p-PKC-ι) level. 1H NMR spectroscopy was employed to determine the Lac/Cr ratio.

RESULTS

The DNA damage increased in a radiation dose-dependent manner (p < 0.05). With the increase in X-ray irradiation, the apoptotic rate also increased (C6, p < 0.01; U251, p < 0.05), and the p-PKC-ι level decreased (C6, p < 0.01; U251, p < 0.05). The p-PKC-ι level negatively correlated with apoptosis, whereas the Lac/Cr ratio positively correlated with the p-PKC-ι level.

CONCLUSION

The Lac/Cr ratio decreases with an increase in X-ray irradiation and thus can be used as a biomarker to reflect the effects of X-ray irradiation in glioma cells.

Roles of partitioning-defective protein 6 (Par6) and its complexes in the proliferation, migration and invasion of cancer cells

A pivotal regulator of cell polarity and homeostasis, partitioning-defective protein 6 (Par6) forms multicomponent complexes that not only regulate cell polarity and stabilize cell morphology, but have also been demonstrated to participate in the proliferation, migration and invasion of cancer cells. The transforming growth factor (TGF)-β and extracellular signal-regulated kinase (Erk) 1/2 pathways are the most thoroughly studied pathways involving Par6 in many cancers. Aurothiomalate has been used to disrupt the interaction between Par6 and atypical protein kinase C within the multicomponent complexes, and has been shown to effectively block transformed growth and metastasis in vitro and/or in vivo in a variety of cancers, including pancreatic, prostate and lung cancers, as well as alveolar rhabdomyosarcoma. It is likely that with further revelations regarding the critical roles of Par6 in cancer initiation, progression and metastasis, targeted therapies against Par6 will be discovered and prove effective preclinically, and hopefully clinically, in cancer treatment.

A proof-of-concept trial of protein kinase C iota inhibition with auranofin for the paclitaxel-induced acute pain syndrome

PURPOSE

Paclitaxel causes the paclitaxel-induced acute pain (PIAP) syndrome. Based on preclinical data, we hypothesized that the protein kinase C (PKC) iota inhibitor, auranofin (a gold salt used for other pain conditions), palliates this pain.

METHODS

In a randomized, double-blinded manner, patients who had suffered this syndrome were assigned a one-time dose of auranofin 6 mg orally on day #2 of the chemotherapy cycle (post-paclitaxel) versus placebo. Patients completed the Brief Pain Inventory and a pain diary on days 2 through 8 and at the end of the cycle. The primary endpoint was pain scores, as calculated by area under the curve, in response to "Please rate your pain by circling the one number that best describes your pain at its worse in the last 24 hours."

RESULTS

Thirty patients were enrolled. For the primary endpoint, mean area under the curve of 55 units (standard deviation 19) and 61 units (standard deviation 22) were observed in auranofin-treated and placebo-exposed patients, respectively (p = 0.44). On day 8 and at the end of the cycle, pain scores in auranofin-treated patients were more favorable, although differences were not statistically significant.

CONCLUSIONS

In the dose schedule studied, auranofin did not palliate the PIAP syndrome, but delayed beneficial trends suggest further study for this indication.

Pediatric soft tissue tumor pathology: A happy morpho-molecular union

Since its foundation by remarkably talented and insightful individuals, prominently including Pepper Dehner, pediatric soft tissue tumor pathology has developed at an immense rate. The morphologic classification of tumoral entities has extensively been corroborated, but has also evolved with refinement or realignment of these classifications, through accruing molecular data, with many derivative ancillary diagnostic assays now already well-established. Tumors of unclear histogenesis, classically morphologically undifferentiated, are prominent amongst pediatric sarcomas, however, the classes of undifferentiated round- or spindle-cell-tumors-not-otherwise-specified are being dismantled gradually with the identification of their molecular underpinnings. Within recent years, for example, numerous subcategories of 'Ewing-like' round cell sarcoma have emerged. Such advances have provided the basis for novel diagnostic and prognostic sub-classifications. Efforts at defining cell- or lineage-of-origin for several tumor types have produced interesting insights especially for rhabdomyosarcoma. The remarkably early onset of pediatric sarcomas defies the theory necessitating stochastic accumulation of several somatic mutations for cancer development and indeed, these tumors may be remarkably genomically stable, often belying their aggressive nature. Much is coming to light recently regarding the role of epigenetic modifications in the evolution of these sarcomas. Indeed the morphologic features of embryonal tumors generally (not just sarcomas) may be highly reminiscent of arrested differentiation, and given the tight epigenetic regulation of cell fate determination and cell identity maintenance, a theory of epigenetically-driven oncogenesis sits easily with these tumors. The age-delimited distinct biologies of 'pediatric' and adult GIST are intriguing, particularly, the SDH-deficient 'pediatric' form, driven by a metabolic defect, but resulting in epigenetic dysregulation with genome-wide DNA methylation changes. There is little doubt that many of the gaps in our understanding of pediatric sarcoma biology will be filled by a deeper appreciation of the role of dysregulated epigenetics including chromatin biology, perhaps best exemplified in malignant rhabdoid tumor. The field of pediatric soft tissue tumor pathology grows ever more interesting. Importantly though, it must be emphasized, that none of this progress could have occurred, or indeed continue, without the initial step of accurate diagnosis, founded solidly on morphology - thank you Pepper for your unparalleled contributions to this field! The opportunity to be your apprentice for five years has been a bigger and more positive influence than words can express.

Current status of treatment for pediatric rhabdomyosarcoma in the USA and Japan

This article reviews the current status of treatment for children with rhabdomyosarcoma, according to the four risk groups. Low-risk subgroup A: the Children's Oncology Group in the USA recently performed a clinical trial consisting of a chemotherapy regimen with a shortened treatment period and a reduced drug dosage. Patients in this group received only four cycles of vincristine and actinomycin D (VA) after four cycles of vincristine, actinomycin D, and cyclophosphamide (VAC) with cyclophosphamide (CPM) 1.2 g/m(2) and their outcome was no worse than that obtained with previous regimens. Low-risk subgroup B: although marked improvement in survival was seen with an intensive VAC regimen with CPM 2.2 g/m(2) /cycle (Intergroup Rhabdomyosarcoma Study [IRS]-V, 1997-2004), the total dose of CPM in this regimen caused serious and fatal hepatic veno-occlusive disease during treatment and probably cannot avoid infertility or possible secondary cancer as a late effect. Thereafter, a reduced-dose regimen consisting of four cycles of VAC with CPM 1.2 g/m(2) followed by 12 cycles of VA was investigated in the next study, but the outcome appeared to be worse than in IRS-V. Intermediate-risk group: no significant difference was found between VAC/vincristine, topotecan and cyclophispahamide (VTC) and intensive VAC in IRS-V. The results of a subsequent regimen of VAC with CPM 1.2 g/m(2) alternating with vincristine and irinotecan are awaited. High-risk group: overall survival is approximately 30% and has not improved over the last 25 years. Although 18 month failure-free survival (FFS) was improved with an intensive combination therapy regimen, 36 month FFS dropped to 32% and thus better novel approaches or additive treatments are needed.

PRKCI negatively regulates autophagy via PIK3CA/AKT-MTOR signaling

The atypical protein kinase C isoform PRKC iota (PRKCI) plays a key role in cell proliferation, differentiation, and carcinogenesis, and it has been shown to be a human oncogene. Here, we show that PRKCI overexpression in U2OS cells impaired functional autophagy in normal or cell stress conditions, as characterized by decreased levels of light chain 3B-II protein (LC3B-II) and weakened degradation of endogenous and exogenous autophagic substrates. Conversely, PRKCI knockdown by small interference RNA resulted in opposite effects. Additionally, we identified two novel PRKCI mutants, PRKCI(L485M) and PRKCI(P560R), which induced autophagy and exhibited dominant negative effects. Further studies indicated that PRKCI knockdown-mediated autophagy was associated with the inactivation of phosphatidylinositol 3-kinase alpha/AKT-mammalian target of rapamycin (PIK3CA/AKT-MTOR) signaling. These data underscore the importance of PRKCI in the regulation of autophagy. Moreover, the finding may be useful in treating PRKCI-overexpressing carcinomas that are characterized by increased levels of autophagy.

Targeting protein kinase C in sarcoma

Protein kinase C (PKC) is a family of serine/threonine tyrosine kinases that regulate many cellular processes including division, proliferation, survival, anoikis and polarity. PKC is abundant in many human cancers and aberrant PKC signalling has been demonstrated in cancer models. On this basis, PKC has become an attractive target for small molecule inhibition within oncology drug development programmes. Sarcoma is a heterogeneous group of mesenchymal malignancies. Due to their relative insensitivity to conventional chemotherapies and the increasing recognition of the driving molecular events of sarcomagenesis, sarcoma provides an excellent platform to test novel therapeutics. In this review we provide a structure-function overview of the PKC family, the rationale for targeting these kinases in sarcoma and the state of play with regard to PKC inhibition in the clinic.

Protein kinase Cδ promotes proliferation and induces malignant transformation in skeletal muscle

In this paper, we investigated the isoform-specific roles of certain protein kinase C (PKC) isoforms in the regulation of skeletal muscle growth. Here, we provide the first intriguing functional evidence that nPKCδ (originally described as an inhibitor of proliferation in various cells types) is a key player in promoting both in vitro and in vivo skeletal muscle growth. Recombinant overexpression of a constitutively active nPKCδ in C2C12 myoblast increased proliferation and inhibited differentiation. Conversely, overexpression of kinase-negative mutant of nPKCδ (DN-nPKCδ) markedly inhibited cell growth. Moreover, overexpression of nPKCδ also stimulated in vivo tumour growth and induced malignant transformation in immunodeficient (SCID) mice whereas that of DN-nPKCδ suppressed tumour formation. The role of nPKCδ in the formation of rhabdomyosarcoma was also investigated where recombinant overexpression of nPKCδ in human rhabdomyosarcoma RD cells also increased cell proliferation and enhanced tumour formation in mouse xenografts. The other isoforms investigated (PKCα, β, ε) exerted only minor (mostly growth-inhibitory) effects in skeletal muscle cells. Collectively, our data introduce nPKCδ as a novel growth-promoting molecule in skeletal muscles and invite further trials to exploit its therapeutic potential in the treatment of skeletal muscle malignancies.

IL-4 receptor blockade abrogates satellite cell: rhabdomyosarcoma fusion and prevents tumor establishment

Tumor cells of the muscle-related cancer alveolar rhabdomyosarcoma (aRMS) have dysregulated terminal myogenic differentiation that is characterized by continuous proliferation, decreased capacity to express markers of terminal differentiation, and inability of tumor cells to fuse to one another in the manner seen for normal myoblasts. Whether aRMS tumor cells can fuse with normal myogenic progenitors such as skeletal muscle stem cells (satellite cells) or myoblasts is unknown, as is the biological effect of fusion events if the phenomenon occurs. To study this possibility, we isolated primary satellite cells harboring a lacZ Cre-LoxP reporter gene for coculture with murine aRMS primary tumor cells expressing Cre. Results of in vitro and in vivo experiments demonstrated tumor cell-muscle cell progenitor fusion events as well as accelerated rates of tumor establishment and progression when satellite cells and derived muscle progenitors were coinjected with tumor cells in an orthotopic allograft model. Interleukin 4 receptor (IL-4R) blocking antibody treatment reversed fusion events in vitro and blocked tumor initiation and progression in vivo. Taken together, this study supports a potential role of tumor cell-host cell fusion and the strong therapeutic potential of IL-4R blockade to prevent the establishment of RMS tumors at new anatomical sites.

New insights into signalling-pathway alterations in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children and young adults. Several recent studies have shed new light on the alterations in signalling pathways and the downstream effects of these pathway alterations in RMS. Many of these effects converge on the fibroblast growth factor and insulin-like growth-factor pathways. These new findings improve the current understanding of RMS, thus offering novel potential therapeutic targets and strategies that may improve the outcome for patients with RMS.

MicroRNAs and epigenetic mechanisms of rhabdomyosarcoma development

Rhabdomyosarcoma is the most common type of soft tissue sarcoma in children. Two main subtypes of rhabdomyosarcoma with different molecular pattern and distinct clinical behaviour may be identified - embryonal and alveolar rhabdomyosarcoma. All types of rhabdomyosarcoma are believed to be of myogenic origin as they express high levels of myogenesis-related factors. They all, however, fail to undergo a terminal differentiation which results in tumour formation. In the aberrant regulation of myogenesis in rhabdomyosarcoma, microRNAs and epigenetic factors are particularly involved. Indeed, these mediators seem to be even more significant for the development of rhabdomyosarcoma than canonical myogenic transcription factors like MyoD, a master regulatory switch for myogenesis. Therefore, in this review we focus on the regulation of rhabdomyosarcoma progression by microRNAs, and especially on microRNAs of the myo-miRNAs family (miR-1, -133a/b and -206), other well-known myogenic regulators like miR-29, and on microRNAs recently recognized to play a role in the differentiation of rhabdomyosarcoma, such as miR-450b-5p or miR-203. We also review changes in epigenetic modifiers associated with rhabdomyosarcoma, namely histone deacetylases and methyltransferases, especially from the Polycomp Group, like Yin Yang1 and Enhancer of Zeste Homolog2. Finally, we summarize how the functioning of these molecules can be affected by oxidative stress and how antioxidative enzymes can influence the development of this tumour. This article is part of a Directed Issue entitled: Rare Cancers.

PKCλ/ι signaling promotes triple-negative breast cancer growth and metastasis

Triple-negative breast cancer (TNBC) is a distinct breast cancer subtype defined by the absence of estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2/neu), and the patients with TNBC are often diagnosed with higher rates of recurrence and metastasis. Because of the absence of ER, PR and HER2/neu expressions, TNBC patients are insensitive to HER2-directed and endocrine therapies available for breast cancer treatment. Here, we report that expression of atypical protein kinase C isoform, PKCλ/ι, significantly increased and activated in all invasive breast cancer (invasive ductal carcinoma or IDC) subtypes including the TNBC subtype. Because of the lack of targeted therapies for TNBC, we choose to study PKCλ/ι signaling as a potential therapeutic target for TNBC. Our observations indicated that PKCλ/ι signaling is highly active during breast cancer invasive progression, and metastatic breast cancers, the advanced stages of breast cancer disease that developed more frequently in TNBC patients, are also characterized with high levels of PKCλ/ι expression and activation. Functional analysis in experimental mouse models revealed that depletion of PKCλ/ι significantly reduces TNBC growth as well as lung metastatic colonization. Furthermore, we have identified a PKCλ/ι-regulated gene signature consisting of 110 genes, which are significantly associated with indolent to invasive progression of human breast cancer and poor prognosis. Mechanistically, cytokines such as TGFβ and IL1β could activate PKCλ/ι signaling in TNBC cells and depletion of PKCλ/ι impairs NF-κB p65 (RelA) nuclear localization. We observed that cytokine-PKCλ/ι-RelA signaling axis, at least in part, involved in modulating gene expression to regulate invasion of TNBC cells. Overall, our results indicate that induction and activation of PKCλ/ι promote TNBC growth, invasion and metastasis. Thus, targeting PKCλ/ι signaling could be a therapeutic option for breast cancer, including the TNBC subtype.

Atypical protein kinase Cι as a human oncogene and therapeutic target

Protein kinase inhibitors represent a major class of targeted therapeutics that has made a positive impact on treatment of cancer and other disease indications. Among the promising kinase targets for further therapeutic development are members of the Protein Kinase C (PKC) family. The PKCs are central components of many signaling pathways that regulate diverse cellular functions including proliferation, cell cycle, differentiation, survival, cell migration, and polarity. Genetic manipulation of individual PKC isozymes has demonstrated that they often fulfill distinct, nonredundant cellular functions. Participation of PKC members in different intracellular signaling pathways reflects responses to varying extracellular stimuli, intracellular localization, tissue distribution, phosphorylation status, and intermolecular interactions. PKC activity, localization, phosphorylation, and/or expression are often altered in human tumors, and PKC isozymes have been implicated in various aspects of transformation, including uncontrolled proliferation, migration, invasion, metastasis, angiogenesis, and resistance to apoptosis. Despite the strong relationship between PKC isozymes and cancer, to date only atypical PKCiota has been shown to function as a bona fide oncogene, and as such is a particularly attractive therapeutic target for cancer treatment. In this review, we discuss the role of PKCiota in transformation and describe mechanism-based approaches to therapeutically target oncogenic PKCiota signaling in cancer.

Cell-cycle dependent expression of a translocation-mediated fusion oncogene mediates checkpoint adaptation in rhabdomyosarcoma

Rhabdomyosarcoma is the most commonly occurring soft-tissue sarcoma in childhood. Most rhabdomyosarcoma falls into one of two biologically distinct subgroups represented by alveolar or embryonal histology. The alveolar subtype harbors a translocation-mediated PAX3:FOXO1A fusion gene and has an extremely poor prognosis. However, tumor cells have heterogeneous expression for the fusion gene. Using a conditional genetic mouse model as well as human tumor cell lines, we show that that Pax3:Foxo1a expression is enriched in G₂ and triggers a transcriptional program conducive to checkpoint adaptation under stress conditions such as irradiation in vitro and in vivo. Pax3:Foxo1a also tolerizes tumor cells to clinically-established chemotherapy agents and emerging molecularly-targeted agents. Thus, the surprisingly dynamic regulation of the Pax3:Foxo1a locus is a paradigm that has important implications for the way in which oncogenes are modeled in cancer cells.

Rare childhood cancers can be paradigms from which important new principles can be discerned. The childhood muscle cancer rhabdomyosarcoma is no exception, having been the focus of the original 1969 description by Drs. Li and Fraumeni of a syndrome now know to be commonly caused by underlying p53 tumor suppressor loss-of-function. In our studies using a conditional genetic mouse model of alveolar rhabdomyosarcoma in conjunction with human tumor cell lines, we have uncovered that the expression level of a translocation-mediated fusion gene, Pax3:Foxo1a, is dynamic and varies during the cell cycle. Our studies support that Pax3:Foxo1a facilitate the yeast-related process of checkpoint adaptation under stresses such as irradiation. The broader implication of our studies is that distal cis elements (promoter-influencing regions of DNA) may be critical to fully understanding the function of cancer-associated translocations.

ATF2 knockdown reinforces oxidative stress-induced apoptosis in TE7 cancer cells

Cancer cells showing low apoptotic effects following oxidative stress-induced DNA damage are mainly affected by growth arrest. Thus, recent studies focus on improving anti-cancer therapies by increasing apoptosis sensitivity. We aimed at identifying a universal molecule as potential target to enhance oxidative stress-based anti-cancer therapy through a switch from cell cycle arrest to apoptosis. A cDNA microarray was performed with hydrogen peroxide-treated oesophageal squamous epithelial cancer cells TE7. This cell line showed checkpoint activation via p21^WAF1, but low apoptotic response following DNA damage. The potential target molecule was chosen depended on the following demands: it should regulate DNA damage response, cell cycle and apoptosis. As the transcription factor ATF2 is implicated in all these processes, we focused on this protein. We investigated checkpoint activation via ATF2. Indeed, ATF2 knockdown revealed ATF2-triggered p21^WAF1 protein expression, suggesting p21^WAF1 transactivation through ATF2. Using chromatin immunoprecipitation (ChIP), we identified a hitherto unknown ATF2-binding sequence in the p21^WAF1 promoter. p-ATF2 was found to interact with p-c-Jun, creating the AP-1 complex. Moreover, ATF2 knockdown led to c-Jun downregulation. This suggests ATF2-driven induction of c-Jun expression, thereby enhancing ATF2 transcriptional activity via c-Jun-ATF2 heterodimerization. Notably, downregulation of ATF2 caused a switch from cell cycle arrest to reinforced apoptosis, presumably via p21^WAF1 downregulation, confirming the importance of ATF2 in the establishment of cell cycle arrest. 1-Chloro-2,4-dinitrobenzene also led to ATF2-dependent G2/M arrest, suggesting that this is a general feature induced by oxidative stress. As ATF2 knockdown also increased apoptosis, we propose ATF2 as a target for combined oxidative stress-based anti-cancer therapies.

Proof-of-concept rare cancers in drug development: the case for rhabdomyosarcoma

Rare diseases typically affect fewer than 200,000 patients annually, yet because thousands of rare diseases exist, the cumulative impact is millions of patients worldwide. Every form of childhood cancer qualifies as a rare disease-including the childhood muscle cancer, rhabdomyosarcoma (RMS). The next few years promise to be an exceptionally good era of opportunity for public-private collaboration for rare and childhood cancers. Not only do certain governmental regulation advantages exist, but these advantages are being made permanent with special incentives for pediatric orphan drug-product development. Coupled with a growing understanding of sarcoma tumor biology, synergy with pharmaceutical muscle disease drug-development programs, and emerging publically available preclinical and clinical tools, the outlook for academic-community-industry partnerships in RMS drug development looks promising.

Protein kinase Cα suppresses Kras-mediated lung tumor formation through activation of a p38 MAPK-TGFβ signaling axis

Protein kinase C alpha (PKCα) can activate both pro- and anti-tumorigenic signaling depending upon cellular context. Here, we investigated the role of PKCα in lung tumorigenesis in vivo. Gene expression data sets revealed that primary human non-small lung cancers (NSCLC) express significantly decreased PKCα levels, indicating that loss of PKCα expression is a recurrent event in NSCLC. We evaluated the functional relevance of PKCα loss during lung tumorigenesis in three murine lung adenocarcinoma models (LSL-Kras, LA2-Kras and urethane exposure). Genetic deletion of PKCα resulted in a significant increase in lung tumor number, size, burden and grade, bypass of oncogene-induced senescence, progression from adenoma to carcinoma and a significant decrease in survival in vivo. The tumor promoting effect of PKCα loss was reflected in enhanced Kras-mediated expansion of bronchio-alveolar stem cells (BASCs), putative tumor-initiating cells, both in vitro and in vivo. LSL-Kras/Prkca(-/-) mice exhibited a decrease in phospho-p38 MAPK in BASCs in vitro and in tumors in vivo, and treatment of LSL-Kras BASCs with a p38 inhibitor resulted in increased colony size indistinguishable from that observed in LSL-Kras/Prkca(-/-) BASCs. In addition, LSL-Kras/Prkca(-/-) BASCs exhibited a modest but reproducible increase in TGFβ1 mRNA, and addition of exogenous TGFβ1 to LSL-Kras BASCs results in enhanced growth similar to untreated BASCs from LSL-Kras/Prkca(-/-) mice. Conversely, a TGFβR1 inhibitor reversed the effects of PKCα loss in LSL-Kras/Prkca(-/-) BASCs. Finally, we identified the inhibitors of DNA binding (Id) Id1-3 and the Wilm's Tumor 1 as potential downstream targets of PKCα-dependent tumor suppressor activity in vitro and in vivo. We conclude that PKCα suppresses tumor initiation and progression, at least in part, through a PKCα-p38MAPK-TGFβ signaling axis that regulates tumor cell proliferation and Kras-induced senescence. Our results provide the first direct evidence that PKCα exhibits tumor suppressor activity in the lung in vivo.

Adenosine-binding motif mimicry and cellular effects of a thieno[2,3-d]pyrimidine-based chemical inhibitor of atypical protein kinase C isoenzymes

The aPKC [atypical PKC (protein kinase C)] isoforms ι and ζ play crucial roles in the formation and maintenance of cell polarity and represent attractive anti-oncogenic drug targets in Ras-dependent tumours. To date, few isoform-specific chemical biology tools are available to inhibit aPKC catalytic activity. In the present paper, we describe the identification and functional characterization of potent and selective thieno[2,3-d]pyrimidine-based chemical inhibitors of aPKCs. A crystal structure of human PKCι kinase domain bound to a representative compound, CRT0066854, reveals the basis for potent and selective chemical inhibition. Furthermore, CRT0066854 displaces a crucial Asn-Phe-Asp motif that is part of the adenosine-binding pocket and engages an acidic patch used by arginine-rich PKC substrates. We show that CRT0066854 inhibits the LLGL2 (lethal giant larvae 2) phosphorylation in cell lines and exhibits phenotypic effects in a range of cell-based assays. We conclude that this compound can be used as a chemical tool to modulate aPKC activity in vitro and in vivo and may guide the search for further aPKC-selective inhibitors.

PKC signaling in glioblastoma

Glioblastoma Multiforme (GBM) is the most aggressive brain tumor characterized by intratumoral heterogeneity at cytopathological, genomic and transcriptional levels. Despite the efforts to develop new therapeutic strategies the median survival of GBM patients is 12-14 months. Results from large-scale gene expression profile studies confirmed that the genetic alterations in GBM affect pathways controlling cell cycle progression, cellular proliferation and survival and invasion ability, which may explain the difficulty to treat GBM patients. One of the signaling pathways that contribute to the aggressive behavior of glioma cells is the protein kinase C (PKC) pathway. PKC is a family of serine/threonine-specific protein kinases organized into three groups according the activating domains. Due to the variability of actions controlled by PKC isoforms, its contribution to the development of GBM is poorly understood. This review intends to highlight the contribution of PKC isoforms to proliferation, survival and invasive ability of glioma cells.