Repression of cancer cell senescence by PKCι

Polarity in breast development and cancer

Mammary gland development and breast cancer progression are associated with extensive remodeling of epithelial tissue architecture. Apical-basal polarity is a key feature of epithelial cells that coordinates key elements of epithelial morphogenesis including cell organization, proliferation, survival, and migration. In this review we discuss advances in our understanding of how apical-basal polarity programs are used in breast development and cancer. We describe cell lines, organoids, and in vivo models commonly used for studying apical-basal polarity in breast development and disease and discuss advantages and limitations of each. We also provide examples of how core polarity proteins regulate branching morphogenesis and lactation during development. We describe alterations to core polarity genes in breast cancer and their associations with patient outcomes. The impact of up- or down-regulation of key polarity proteins in breast cancer initiation, growth, invasion, metastasis, and therapeutic resistance are discussed. We also introduce studies demonstrating that polarity programs are involved in regulating the stroma, either through epithelial-stroma crosstalk, or through signaling of polarity proteins in non-epithelial cell types. Overall, a key concept is that the function of individual polarity proteins is highly contextual, depending on developmental or cancer stage and cancer subtype.

Targeting Protein Kinase C for Cancer Therapy

Simple Summary

The protein kinase C (PKC) family belongs to serine-threonine kinases and consists of several subtypes. Increasing evidence suggests that PKCs are critical players in carcinogenesis. Interestingly, PKCs exert both promotive and suppressive effects on tumor cell growth and metastasis, which have attracted immense attention. Herein, we systematically review the current advances in the structure, regulation and biological functions of PKCs, especially the relationship of PKCs with anti-cancer therapy-induced cell death, including the current knowledge of PKCs function in tumor metabolism and microenvironment. Moreover, we discuss the potential role of PKCs as a target for therapeutic intervention in cancer from basic research and clinical trials.

Abstract

Protein kinase C (PKC) isoforms, a group of serine-threonine kinases, are important regulators in carcinogenesis. Numerous studies have demonstrated that PKC isoforms exert both positive and negative effects on cancer cell demise. In this review, we systematically summarize the current findings on the architecture, activity regulation and biological functions of PKCs, especially their relationship with anti-cancer therapy-induced cell death. Additionally, we elaborate on current knowledge of the effects of PKCs on tumor metabolism and microenvironment, which have gained increasing attention in oncology-related areas. Furthermore, we underscore the basic experimental and clinical implications of PKCs as a target for cancer therapy to evaluate their therapeutic benefits and potential applications.

Detection and Clinical Value of Circulating Tumor Cells as an Assisted Prognostic Marker in Colorectal Cancer Patients

BACKGROUND

Circulating tumor cells (CTCs) are cells that have been shed into the vasculature from a primary tumor and circulate in the bloodstream. It has been suggested that detecting CTCs could help the clinician to detect early metastasis or recurrence more effectively. This trial sets out to assess the detection and clinical value of CTCs as an assisted prognostic marker in patients with colon cancer and rectal cancer.

METHODS

A prospective cohort of patients with colorectal cancer (CRC) was enrolled from July 2015 to February 2018 in Shanghai Minimally Invasive Surgery Center, Shanghai, China. In this study, 149 patients with CRC were enrolled and underwent surgical treatment. There were 79 cases of colon cancer and 70 cases of rectal cancer, including 93 males and 56 females. To investigate the correlativity and clinical value of CTCs, the patients were statistically analyzed in different subgroups: colon cancer group vs rectal cancer group, and left hemicolon cancer group vs right hemicolon cancer group.

RESULTS

The results of analysis comparing CTC counts and clinical pathological features in colon and rectal cancer indicated that with increased tumor stage, the number of CTCs also increased, with significant statistical differences. CTC counts in patients with colon and rectal cancer showed positive correlations with TNM staging (P=0.001, 0.013, respectively), T staging (P=0.021, 0.001), N staging (P=0.014, 0.035) and M staging (P=0.018, 0.203). Detection of serum biomarkers in CTC-positive and CTC-negative groups indicated a significantly increasing expression in the CTC-positive group. To confirm the correlations between CTCs and histoembryological differences, analysis was conducted with the patients in two subgroups: left hemicolon cancer group and right hemicolon cancer group. The results showed that the positive rate of CTCs increased in both groups with the increase in tumor stage. The survival analysis indicated that there was a steep gradient in survival in the follow-up period, particularly in the CTC-positive group (P=0.000). Risk assessment curves showed that the change escalated more rapidly in the CTC-positive group. Furthermore, with the increase in T stage, changes in the survival curve and risk curve escalated more rapidly in the CTC-positive group.

CONCLUSION

It was confirmed that in the left hemicolon cancer group, a much higher coincidence rate could be found on CTC-positive rate and clinicopathological features, than in the right hemicolon cancer group. The sensitivity of CTCs may be related to the histoembryological location of the tumor, lymphatic metastasis and the depth of infiltration. Monitoring CTCs may have value in evaluating clinical staging and estimating clinical prognosis.

The therapeutic potential of Aurora kinases targeting in glioblastoma: from preclinical research to translational oncology

Glioblastoma is the most common aggressive primary brain tumor. Standard care includes maximal safe surgical resection, radiation, and chemotherapy with temozolomide. However, the impact of this therapeutic approach on patient survival is disappointing and poor outcomes are frequently observed. Therefore, new therapeutic targets are needed to treat this potentially deadly tumor. Aurora kinases are one of today's most sought-after classes of therapeutic targets to glioblastoma therapy. They are a family of proteins composed of three members: Aurora-A, Aurora-B, and Aurora-C that play different roles in the cell division through regulation of chromosome segregation. Deregulation of these genes has been reported in glioblastoma and a progressive number of studies have shown that inhibition of these proteins could be a promising strategy for the treatment of this tumor. This review discusses the preclinical and early clinical findings on the potential use of the Aurora kinases as new targets for the treatment of glioblastoma. KEY MESSAGES: GBM is a very aggressive tumor with limited therapeutic options. Aurora kinases are a family of serine/threonine kinases implicated in GBM pathology. Aurora kinases are critical for glioblastoma cell growth, apoptosis, and chemoresistance. Inhibition of Aurora kinases has a synergistic or sensitizing effect with chemotherapy drugs, radiotherapy, or with other targeted molecules in GBM. Several Aurora kinase inhibitors are currently in clinical trials.

Preclinical testing of 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide: a potent protein kinase C-ι inhibitor as a potential prostate carcinoma therapeutic

Protein kinase C-iota (PKC-ι) is an oncogene overexpressed in many cancer cells including prostate, breast, ovarian, melanoma, and glioma. Previous in-vitro studies have shown that 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide (ICA-1s), a PKC-ι specific inhibitor, is effective against some cancer cell lines by decreasing cell growth and inducing apoptosis. To assess ICA-1s as a possible therapeutic, in-vivo studies using a murine model were performed. ICA-1s was tested for stability in blood serum and results demonstrated that ICA-1s was stable in human plasma at 25 and 37°C over a course of 2 h. Toxicity of ICA-1s was tested for both acute and subacute exposure. The acute exposure showed patient surviving after 48 h of doses ranging from 5 to 5000 mg/kg. Subacute tests exposed the patients to 14 days of treatment and were followed by serum and tissue collection. Aspartate aminotransferase, alkaline phosphatase, γ-glutamyl transpeptidase, troponin, and C-reactive protein serum levels were measured to assess organ function. ICA-1s in plasma serum was measured over the course of 24 h for both oral and intravenous treatments. Heart, liver, kidney, and brain tissues were analyzed for accumulation of ICA-1s. Finally, athymic nude mice were xenografted with DU-145 prostate cancer cells. After tumors reached ~0.2 cm², they were either treated with ICA-1s or left as control and measured for 30 days or until the tumor reached 2 cm². Results showed tumors in treated mice grew at almost half the rate as untreated tumors, showing a significant reduction in growth. In conclusion, ICA-1s is stable, shows low toxicity, and is a potential therapeutic for prostate carcinoma tumors.

An Interplay between Senescence, Apoptosis and Autophagy in Glioblastoma Multiforme-Role in Pathogenesis and Therapeutic Perspective

Autophagy, cellular senescence, programmed cell death and necrosis are key responses of a cell facing a stress. These effects are partly interconnected, but regulation of their mutual interactions is not completely clear. That regulation seems to be especially important in cancer cells, which have their own program of development and demand more nutrition and energy than normal cells. Glioblastoma multiforme (GBM) belongs to the most aggressive and most difficult to cure cancers, so studies on its pathogenesis and new therapeutic strategies are justified. Using an animal model, it was shown that autophagy is required for GBM development. Temozolomide (TMZ) is the key drug in GBM chemotherapy and it was reported to induce senescence, autophagy and apoptosis in GBM. In some GBM cells, TMZ induces small toxicity despite its significant concentration and GBM cells can be intrinsically resistant to apoptosis. Resveratrol, a natural compound, was shown to potentiate anticancer effect of TMZ in GBM cells through the abrogation G2-arrest and mitotic catastrophe resulting in senescence of GBM cells. Autophagy is the key player in TMZ resistance in GBM. TMZ can induce apoptosis due to selective inhibition of autophagy, in which autophagic vehicles accumulate as their fusion with lysosomes is blocked. Modulation of autophagic action of TMZ with autophagy inhibitors can result in opposite outcomes, depending on the step targeted in autophagic flux. Studies on relationships between senescence, autophagy and apoptosis can open new therapeutic perspectives in GBM.

Protein kinase C downregulation induces senescence via FoxO3a inhibition in HCT116 and HEK293 cells

We investigated the impact of protein kinase C (PKC) on cellular senescence. The PKC activity and expression of conventional PKC (cPKC) and atypical PKC (aPKC) isoforms decreased during replicative senescence in IMR-90 cells. Forced inhibition of cPKC or aPKC induced the activation of senescence markers, including senescence-associated β-galactosidase activity and reactive oxygen species (ROS)-p53-p21^Cip1/WAF1 axis in HCT116 and HEK293 cells. PKC inhibition triggered the nuclear exportation of FoxO3a via stimulation of AKT-mediated phosphorylation of FoxO3a, and thereby decreased the transcription of FoxO3a target genes. Conversely, ectopic expression of the PKC isoforms led to stimulation of the nuclear import of FoxO3a and expression of the FoxO3a target genes. Ectopic FoxO3a expression attenuated ROS accumulation and senescent phenotypes induced by PKC inhibition. Therefore, this study suggests for the first time that downregulation of PKC induces senescence through the AKT-FoxO3a-ROS-p53-p21^Cip1/WAF1 pathway in HCT116 and HEK293 cells.

Epithelial cell senescence: an adaptive response to pre-carcinogenic stresses?

Senescence is a cell state occurring in vitro and in vivo after successive replication cycles and/or upon exposition to various stressors. It is characterized by a strong cell cycle arrest associated with several molecular, metabolic and morphologic changes. The accumulation of senescent cells in tissues and organs with time plays a role in organismal aging and in several age-associated disorders and pathologies. Moreover, several therapeutic interventions are able to prematurely induce senescence. It is, therefore, tremendously important to characterize in-depth, the mechanisms by which senescence is induced, as well as the precise properties of senescent cells. For historical reasons, senescence is often studied with fibroblast models. Other cell types, however, much more relevant regarding the structure and function of vital organs and/or regarding pathologies, are regrettably often neglected. In this article, we will clarify what is known on senescence of epithelial cells and highlight what distinguishes it from, and what makes it like, replicative senescence of fibroblasts taken as a standard.

Molecular Signatures Associated with Treatment of Triple-Negative MDA-MB231 Breast Cancer Cells with Histone Deacetylase Inhibitors JAHA and SAHA

Jay Amin hydroxamic acid (JAHA; N8-ferrocenylN¹-hydroxy-octanediamide) is a ferrocene-containing analogue of the histone deacetylase inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA). JAHA's cytotoxic activity on MDA-MB231 triple negative breast cancer (TNBC) cells at 72 h has been previously demonstrated with an IC₅₀ of 8.45 μM. JAHA's lethal effect was found linked to perturbations of cell cycle, mitochondrial activity, signal transduction, and autophagy mechanisms. To glean novel insights on how MDA-MB231 breast cancer cells respond to the cytotoxic effect induced by JAHA, and to compare the biological effect with the related compound SAHA, we have employed a combination of differential display-PCR, proteome analysis, and COMET assay techniques and shown some differences in the molecular signature profiles induced by exposure to either HDACis. In particular, in contrast to the more numerous and diversified changes induced by SAHA, JAHA has shown a more selective impact on expression of molecular signatures involved in antioxidant activity and DNA repair. Besides expanding the biological knowledge of the effect exerted by the modifications in compound structures on cell phenotype, the molecular elements put in evidence in our study may provide promising targets for therapeutic interventions on TNBCs.

Protein kinase C (PKC) isoforms in cancer, tumor promotion and tumor suppression

The AGC family of serine/threonine kinases (PKA, PKG, PKC) includes more than 60 members that are critical regulators of numerous cellular functions, including cell cycle and differentiation, morphogenesis, and cell survival and death. Mutation and/or dysregulation of AGC kinases can lead to malignant cell transformation and contribute to the pathogenesis of many human diseases. Members of one subgroup of AGC kinases, the protein kinase C (PKC), have been singled out as critical players in carcinogenesis, following their identification as the intracellular receptors of phorbol esters, which exhibit tumor-promoting activities. This observation attracted the attention of researchers worldwide and led to intense investigations on the role of PKC in cell transformation and the potential use of PKC as therapeutic drug targets in cancer diseases. Studies demonstrated that many cancers had altered expression and/or mutation of specific PKC genes. However, the causal relationships between the changes in PKC gene expression and/or mutation and the direct cause of cancer remain elusive. Independent studies in normal cells demonstrated that activation of PKC is essential for the induction of cell activation and proliferation, differentiation, motility, and survival. Based on these observations and the general assumption that PKC isoforms play a positive role in cell transformation and/or cancer progression, many PKC inhibitors have entered clinical trials but the numerous attempts to target PKC in cancer has so far yielded only very limited success. More recent studies demonstrated that PKC function as tumor suppressors, and suggested that future clinical efforts should focus on restoring, rather than inhibiting, PKC activity. The present manuscript provides some historical perspectives on the tumor promoting function of PKC, reviewing some of the observations linking PKC to cancer progression, and discusses the role of PKC in the pathogenesis of cancer diseases and its potential usage as a therapeutic target.

Induction of senescence in primary glioblastoma cells by serum and TGFβ

Glioblastoma is the most common type of adult brain tumour and has a median survival after diagnosis of a little more than a year. Glioblastomas have a high frequency of mutations in the TERT promoter and CDKN2A locus that are expected to render them resistant to both replicative and oncogene-induced senescence. However, exposure of PriGO8A primary glioblastoma cells to media with 10% serum induced a senescence-like phenotype characterized by increased senescence-associated β galactosidase activity, PML bodies and p21 and morphological changes typical of senescence. Microarray expression analysis showed that 24 h serum exposure increased the expression of genes associated with the TGFβ pathway. Treatment of PriGO8A cells with TGFβ was sufficient to induce senescence in these cells. The response of PriGO8A cells to serum was dependent on basal expression of the TGFβ activator protein thrombospondin. Primary glioblastoma cells from three additional patients showed a variable ability to undergo senescence in response to serum. However all were able to undergo senescence in response to TGFβ, although for cells from one patient this required concomitant inhibition of Ras pathway signalling. Primary glioblastoma cells therefore retain a functional senescence program that is inducible by acute activation of the TGFβ signalling pathway.

An Allosteric Inhibitor Scaffold Targeting the PIF-Pocket of Atypical Protein Kinase C Isoforms

There is a current and pressing need for improved cancer therapies. The use of small molecule kinase inhibitors and their application in combinatorial regimens represent an approach to personalized targeted cancer therapy. A number of AGC kinases, including atypical Protein Kinase C enzymes (PKCs), are validated drug targets for cancer treatment. Most drug development programs for protein kinases focus on the development of drugs that bind at the ATP-binding site. Alternatively, allosteric drugs have great potential for the development of future innovative drugs. However, the rational development of allosteric drugs poses important challenges because the compounds not only must bind to a given site but also must stabilize forms of the protein with a desired effect at a distant site. Here we describe the development of a new class of compounds targeting a regulatory site (PIF-pocket) present in the kinase domain and provide biochemical and crystallographic data showing that these compounds allosterically inhibit the activity of atypical PKCs. PS432, a representative compound, decreased the rate of proliferation of non-small cell lung cancer cells more potently than aurothiomalate, an atypical PKCι inhibitor currently under evaluation in clinical trials, and significantly reduced tumor growth without side effects in a mouse xenograft model. The druglike chemical class provides ample possibilities for the synthesis of derivative compounds, with the potential to allosterically modulate the activity of atypical PKCs and other kinases.

PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma

Cellular senescence is a tumor suppressor mechanism where cells enter a permanent growth arrest following cellular stress. Oncogene-induced senescence (OIS) is induced in non-malignant cells following the expression of an oncogene or inactivation of a tumor suppressor. Previously, we have shown that protein kinase C iota (PKCι) depletion induces cellular senescence in glioblastoma cells in the absence of a detectable DNA damage response. Here we demonstrate that senescent glioblastoma cells exhibit an aberrant centrosome morphology. This was observed in basal levels of senescence, in p21-induced senescence, and in PKCι depletion-induced senescence. In addition, senescent glioblastoma cells are polyploid, Ki-67 negative and arrest at the G1/S checkpoint, as determined by expression of cell cycle regulatory proteins. These markers are all consistent with cells that have undergone mitotic slippage. Failure of the spindle assembly checkpoint to function properly can lead to mitotic slippage, resulting in the premature exit of mitotic cells into the G1 phase of the cell cycle. Although in G1, these cells have the replicated DNA and centrosomal phenotype of a cell that has entered mitosis and failed to divide. Overall, we demonstrate that PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma cells. To our knowledge, this is the first evidence of markers of mitotic slippage directly in senescent cells by co-staining for senescence-associated β-galactosidase and immunofluorescence markers in the same cell population. We suggest that markers of mitotic slippage be assessed in future studies of senescence to determine the extent of mitotic slippage in the induction of cellular senescence.

PKCiota promotes ovarian tumor progression through deregulation of cyclin E

The high frequency of relapse of epithelial ovarian tumors treated with standard chemotherapy has highlighted the necessity to identify targeted therapies that can improve patient outcomes. The dynamic relationship between Cyclin E and PKCiota frequent overexpression in high-grade ovarian tumors poses a novel pathway for therapeutic investigation. We hypothesized that a PI3K dependent signaling pathway activating PKCiota perpetuates cyclin E deregulation during ovarian tumorigenesis. We observed a positive correlation between PKCiota and cyclin E in a panel of 19 ovarian cancer cell lines. Modulation of cyclin E had no effect on PKCiota knockdown/overexpression however PKCiota differentially regulated cyclin E expression. In the serous ovarian cancer cells (IGROV, OVCAR-3), shPKCiota decreased proliferation, caused a G1 arrest, and significantly prolonged overall survival in xenograft mouse models. In vitro shPKCiota decreased the ability of IGROV cells to grow under anchorage independent conditions and form aberrant acini, which was dependent upon Ad-cyclin E or Ad-LMW-E expression. RPPA analysis of PKCiota wild-type, catalytic active, dominant negative protein isoforms strengthened the association between phospho-PKCiota levels and PI3K pathway activation. Inhibitors of PI3K coordinately decreased phospho-PKCiota and Cyclin E protein levels. In conclusion, we have identified a PI3K/PKCiota/Cyclin E signaling pathway as a therapeutic target during ovarian tumorigenesis.

Atypical protein kinase C induces cell transformation by disrupting Hippo/Yap signaling

Epithelial cells are major sites of malignant transformation. Atypical protein kinase C (aPKC) isoforms are overexpressed and activated in many cancer types. Using normal, highly polarized epithelial cells (MDCK and NMuMG), we report that aPKC gain of function overcomes contact inhibited growth and is sufficient for a transformed epithelial phenotype. In 2D cultures, aPKC induced cells to grow as stratified epithelia, whereas cells grew as solid spheres of nonpolarized cells in 3D culture. aPKC associated with Mst1/2, which uncoupled Mst1/2 from Lats1/2 and promoted nuclear accumulation of Yap1. Of importance, Yap1 was necessary for aPKC-mediated overgrowth but did not restore cell polarity defects, indicating that the two are separable events. In MDCK cells, Yap1 was sequestered to cell-cell junctions by Amot, and aPKC overexpression resulted in loss of Amot expression and a spindle-like cell phenotype. Reexpression of Amot was sufficient to restore an epithelial cobblestone appearance, Yap1 localization, and growth control. In contrast, the effect of aPKC on Hippo/Yap signaling and overgrowth in NMuMG cells was independent of Amot. Finally, increased expression of aPKC in human cancers strongly correlated with increased nuclear accumulation of Yap1, indicating that the effect of aPKC on transformed growth by deregulating Hippo/Yap1 signaling may be clinically relevant.

PKCζ Promotes Breast Cancer Invasion by Regulating Expression of E-cadherin and Zonula Occludens-1 (ZO-1) via NFκB-p65

Atypical Protein Kinase C zeta (PKCζ) forms Partitioning-defective (PAR) polarity complex for apico-basal distribution of membrane proteins essential to maintain normal cellular junctional complexes and tissue homeostasis. Consistently, tumor suppressive role of PKCζ has been established for multiple human cancers. However, recent studies also indicate pro-oncogenic function of PKCζ without firm understanding of detailed molecular mechanism. Here we report a possible mechanism of oncogenic PKCζ signaling in the context of breast cancer. We observed that depletion of PKCζ promotes epithelial morphology in mesenchymal-like MDA-MB-231 cells. The induction of epithelial morphology is associated with significant upregulation of adherens junction (AJ) protein E-cadherin and tight junction (TJ) protein Zonula Occludens-1 (ZO-1). Functionally, depletion of PKCζ significantly inhibits invasion and metastatic progression. Consistently, we observed higher expression and activation of PKCζ signaling in invasive and metastatic breast cancers compared to non-invasive diseases. Mechanistically, an oncogenic PKCζ– NFκB-p65 signaling node might be involved to suppress E-cadherin and ZO-1 expression and ectopic expression of a constitutively active form of NFκB-p65 (S536E-NFκB-p65) significantly rescues invasive potential of PKCζ-depleted breast cancer cells. Thus, our study discovered a PKCζ - NFκB-p65 signaling pathway might be involved to alter cellular junctional dynamics for breast cancer invasive progression.

PKCη promotes senescence induced by oxidative stress and chemotherapy

Senescence is characterized by permanent cell-cycle arrest despite continued viability and metabolic activity, in conjunction with the secretion of a complex mixture of extracellular proteins and soluble factors known as the senescence-associated secretory phenotype (SASP). Cellular senescence has been shown to prevent the proliferation of potentially tumorigenic cells, and is thus generally considered a tumor suppressive process. However, some SASP components may act as pro-tumorigenic mediators on premalignant cells in the microenvironment. A limited number of studies indicated that protein kinase C (PKC) has a role in senescence, with different isoforms having opposing effects. It is therefore important to elucidate the functional role of specific PKCs in senescence. Here we show that PKCη, an epithelial specific and anti-apoptotic kinase, promotes senescence induced by oxidative stress and DNA damage. We further demonstrate that PKCη promotes senescence through its ability to upregulate the expression of the cell cycle inhibitors p21^Cip1 and p27^Kip1 and enhance transcription and secretion of interleukin-6 (IL-6). Moreover, we demonstrate that PKCη creates a positive loop for reinforcing senescence by increasing the transcription of both IL-6 and IL-6 receptor, whereas the expression of IL-8 is specifically suppressed by PKCη. Thus, the presence/absence of PKCη modulates major components of SASP. Furthermore, we show that the human polymorphic variant of PKCη, 374I, that exhibits higher kinase activity in comparison to WT-374V, is also more effective in IL-6 secretion, p21^Cip1 expression and the promotion of senescence, further supporting a role for PKCη in senescence. As there is now considerable interest in senescence activation/elimination to control tumor progression, it is first crucial to reveal the molecular regulators of senescence. This will improve our ability to develop new strategies to harness senescence as a potential cancer therapy in the future.

PTEN loss represses glioblastoma tumor initiating cell differentiation via inactivation of Lgl1

Glioblastoma multiforme is an aggressive and incurable type of brain tumor. A subset of undifferentiated glioblastoma cells, known as glioblastoma tumor initiating cells (GTICs), has an essential role in the malignancy of this disease and also appears to mediate resistance to radiation therapy and chemotherapy. GTICs retain the ability to differentiate into cells with reduced malignant potential, but the signaling pathways controlling differentiation are not fully understood at this time. PTEN loss is a very common in glioblastoma multiforme and leads to aberrant activation of the phosphoinositide 3-kinase pathway. Increased signalling through this pathway leads to activation of multiple protein kinases, including atypical protein kinase C. In Drosophila, active atypical protein kinase C has been shown to promote the self-renewal of neuroblasts, inhibiting their differentiation along a neuronal lineage. This effect is mediated by atypical protein kinase c-mediated phosphorylation and inactivation of Lgl, a protein that was first characterized as a tumour suppressor in Drosophila. The effects of the atypical protein kinase C/Lgl pathway on the differentiation status of GTICs, and its potential link to PTEN loss, have not been assessed previously. Here we show that PTEN loss leads to the phosphorylation and inactivation of Lgl by atypical protein kinase C in glioblastoma cells. Re-expression of PTEN in GTICs promoted their differentiation along a neuronal lineage. This effect was also seen when atypical protein kinase C was knocked down using RNA interference, and when a non-phosphorylatable, constitutively active form of Lgl was expressed in GTICs. Thus PTEN loss, acting via atypical protein kinase C activation and Lgl inactivation, helps to maintain GTICs in an undifferentiated state.

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.

Emerging role of cell polarity proteins in breast cancer progression and metastasis

Breast cancer is a heterogeneous group of diseases that frequently exhibits loss of growth control, and disrupted tissue organization and differentiation. Several recent studies indicate that apical–basal polarity provides a tumor-suppressive function, and that disrupting polarity proteins affects many stages of breast cancer progression from initiation through metastasis. In this review we highlight some of the recent advances in our understanding of the molecular mechanisms by which loss of apical–basal polarity deregulates apoptosis, proliferation, and promotes invasion and metastasis in breast cancer.

Immortality of cell lines: challenges and advantages of establishment

Cellular immortality happens upon impairment of cell-cycle checkpoint pathways (p53/p16/pRb), reactivation or up-regulation of telomerase enzyme, or upregulation of some oncogenes or oncoproteins leading to a higher rate of cell division.There are also some other factors and mechanisms involved in immortalisation, which need to be discovered. Immortalisation of cells derived from different sources and establishment of immortal cell lines has proven useful in understanding the molecular pathways governing cell developmental cascades in eukaryotic, especially human, cells. After the breakthrough of achieving the immortal cells and understanding their critical importance in the field of molecular biology, intense efforts have been dedicated to establish cell lines useful for elucidating the functions of telomerase, developmental lineage of progenitors, self-renewal potency, cellular transformation, differentiation patterns and some bioprocesses, like odontogenesis. Meanwhile, discovering the exact mechanisms of immortality, a major challenge for science yet, is believed to open new gateways toward understanding and treatment of cancer in the long term. This review summarises the methods involved in establishing immortality, its advantages and the challenges still being faced in this field.