SKP2/P27Kip1 pathway is associated with Advanced Ovarian Cancer in Saudi Patients

Inhibition of CDK4/6 as Therapeutic Approach for Ovarian Cancer Patients: Current Evidences and Future Perspectives

Simple Summary

Altered regulation of the cell cycle is a hallmark of cancer. The recent clinical success of the inhibitors of CDK4 and CDK6 has convincingly demonstrated that targeting cell cycle components may represent an effective anti-cancer strategy, at least in some cancer types. However, possible applications of CDK4/6 inhibitors in patients with ovarian cancer is still under evaluation. Here, we describe the possible biological role of CDK4 and CDK6 complexes in ovarian cancer and provide the rationale for the use of CDK4/6 inhibitors in this pathology, alone or in combination with other drugs. This review, coupling basic, preclinical and clinical research studies, could be of great translational value for investigators attempting to design new clinical trials for the better management of ovarian cancer patients.

Abstract

Alterations in components of the cell-cycle machinery are present in essentially all tumor types. In particular, molecular alterations resulting in dysregulation of the G1 to S phase transition have been observed in almost all human tumors, including ovarian cancer. These alterations have been identified as potential therapeutic targets in several cancer types, thereby stimulating the development of small molecule inhibitors of the cyclin dependent kinases. Among these, CDK4 and CDK6 inhibitors confirmed in clinical trials that CDKs might indeed represent valid therapeutic targets in, at least some, types of cancer. CDK4 and CDK6 inhibitors are now used in clinic for the treatment of patients with estrogen receptor positive metastatic breast cancer and their clinical use is being tested in many other cancer types, alone or in combination with other agents. Here, we review the role of CDK4 and CDK6 complexes in ovarian cancer and propose the possible use of their inhibitors in the treatment of ovarian cancer patients with different types and stages of disease.

Possibility of inducing tumor cell senescence during therapy

The treatment options for cancer include surgery, radiotherapy and chemotherapy. However, the traditional approach of high-dose chemotherapy brings tremendous toxic side effects to patients, as well as potentially causing drug resistance. Drug resistance affects cell proliferation, cell senescence and apoptosis. Cellular senescence refers to the process in which cells change from an active proliferative status to a growth-arrested status. There are multiple factors that regulate this process and cellular senescence is activated by various pathways. Senescent cells present specific characteristics, such as an increased cell volume, flattened cell body morphology, ceased cell division and the expression of β-galactosidase. Tumor senescence can be categorized into replicative senescence and premature senescence. Cellular senescence may inhibit the occurrence and development of tumors, serving as an innovative strategy for the treatment of cancer. The present review mainly focuses on senescent biomarkers, methods for the induction of cellular senescence and its possible application in the treatment of cancer.

Quinacrine upregulates p21/p27 independent of p53 through autophagy-mediated downregulation of p62-Skp2 axis in ovarian cancer

We have previously shown that the anti-malarial compound Quinacrine (QC) inhibits ovarian cancer (OC) growth by modulating autophagy. In the present study we extended these studies to identify the molecular pathways regulated by QC to promote apoptosis independent of p53 status in OC. QC exhibited strong anti-cancer properties in OC cell lines in contrast to other anti-malarial autophagy inhibiting drugs. QC treatment selectively upregulated cell cycle inhibitor p21, and downregulated F box protein Skp2 and p62/SQSTM1 expression independent of p53 status. Genetic downregulation of key autophagy protein ATG5 abolished QC-mediated effects on both cell cycle protein p21/Skp2 as well as autophagic cargo protein p62. Furthermore, genetic silencing of p62/SQSTM1 resulted in increased sensitivity to QC-mediated apoptosis, downregulated Skp2 mRNA and increased accumulation of p21 expression. Likewise, genetic knockdown of Skp2 resulted in the upregulation of p21 and p27 and increased sensitivity of OC cells to QC treatment. In contrast, transient overexpression of exogenous p62-HA plasmid rescued the QC-mediated Skp2 downregulation indicating the positive regulation of Skp2 by p62. Collectively, these data indicate that QC-mediated effects on cell cycle proteins p21/Skp2is autophagy-dependent and p53-independent in high grade serious OC cells.

Expression of hsa-let-7b-5p, hsa-let-7f-5p, and hsa-miR-222-3p and their putative targets HMGA2 and CDKN1B in typical and atypical carcinoid tumors of the lung

Typical and atypical carcinoid tumors belong to the neuroendocrine lung tumors. They have low recurrence and proliferation rate, lymph node, and distant metastases. Nevertheless, these tumors have shown a more aggressive behavior. In the last years, microRNAs were screened as new tumor markers for their potential diagnostic and therapeutic relevance. The expression of hsa-let-7b-5p, hsa-let-7f-5p, hsa-miR-222-3p, and their targets HMGA2 (high-mobility group A2) and CDKN1B (cyclin-dependent kynase inhibitor 1B, p27^kip1) was evaluated in this rare small group of patients. We analyzed the clinical data of all typical and atypical carcinoid tumors of patients who underwent surgical operation at Marburg University Hospital (n = 18) from 2000. Quantitative reverse transcription polymerase chain reaction was performed in formalin-fixed paraffin-embedded tumor tissue versus four tumor-free lung tissue samples. HMGA2 was stable or downregulated; only one patient showed a significant overexpression. CDKN1B showed a significant overexpression or a stable level; it was downregulated in two samples only. Hsa-miR-222-3p resulted almost stable or overexpressed except for two samples (significantly downregulated). Hsa-let-7f-5p was stable or overexpressed in the majority of analyzed samples, whereas hsa-let-7b-5p was significantly downregulated. HMGA2 and CDKN1B are differently expressed between atypical and typical carcinoid tumors, thus representing valid biomarkers for the classification of the two tumor groups. Hsa-let-7f-5p and HMGA2 are inversely correlated. Hsa-miR-222-3p does not correlate with its predicted target CDKN1B.

BAG3 promotes proliferation of ovarian cancer cells via post-transcriptional regulation of Skp2 expression

Bcl-2 associated athanogene 3 (BAG3) contains a modular structure, through which BAG3 interacts with a wide range of proteins, thereby affording its capacity to regulate multifaceted biological processes. BAG3 is often highly expressed and functions as a pro-survival factor in many cancers. However, the oncogenic potential of BAG3 remains not fully understood. The cell cycle regulator, S-phase kinase associated protein 2 (Skp2) is increased in various cancers and plays an important role in tumorigenesis. The current study demonstrated that BAG3 promoted proliferation of ovarian cancer cells via upregulation of Skp2. BAG3 stabilized Skp2 mRNA via its 3'-untranslated region (UTR). The current study demonstrated that BAG3 interacted with Skp2 mRNA. In addition, miR-21-5p suppressed Skp2 expression, which was compromised by forced BAG3 expression. These results indicated that at least some oncogenic functions of BAG3 were mediated through posttranscriptional regulation of Skp2 via antagonizing suppressive action of miR-21-5p in ovarian cancer cells.

Nitidine chloride inhibited the expression of S phase kinase-associated protein 2 in ovarian cancer cells

Nitidine chloride (NC) has been reported to exert its anti-tumor activity in various types of human cancers. However, the molecular mechanism of NC-mediated tumor suppressive function is largely unclear. In the current study, we used several approaches such as MTT, FACS, RT-PCR, Western blotting analysis, invasion assay, transfection, to explore the molecular basis of NC-triggered anti-cancer activity. We found that NC inhibited cell growth, induced cell apoptosis, caused cell cycle arrest in ovarian cancer cells. Emerging evidence has demonstrated that Skp2 plays an important oncogenic role in ovarian cancer. Therefore, we also explored whether NC exerts its biologic function via downregulation of Skp2 in ovarian cancer cells. We observed that NC significantly inhibited the expression of Skp2 in ovarian cancer cells. Notably, overexpression of Skp2 abrogated the anti-cancer activity induced by NC in ovarian cancer cells. Consistently, downregulation of Skp2 expression enhanced the sensitivity of ovarian cancer cells to NC treatment. Thus, inactivation of Skp2 by NC could be a novel strategy for the treatment of human ovarian cancer.

APC/C and retinoblastoma interaction: cross-talk of retinoblastoma protein with the ubiquitin proteasome pathway

The ubiquitin (Ub) ligase anaphase promoting complex/cyclosome (APC/C) and the tumour suppressor retinoblastoma protein (pRB) play key roles in cell cycle regulation. APC/C is a critical regulator of mitosis and G₁-phase of the cell cycle whereas pRB keeps a check on proliferation by inhibiting transition to the S-phase. APC/C and pRB interact with each other via the co-activator of APC/C, FZR1, providing an alternative pathway of regulation of G₁ to S transition by pRB using a post-translational mechanism. Both pRB and FZR1 have complex roles and are implicated not only in regulation of cell proliferation but also in differentiation, quiescence, apoptosis, maintenance of chromosomal integrity and metabolism. Both are also targeted by transforming viruses. We discuss recent advances in our understanding of the involvement of APC/C and pRB in cell cycle based decisions and how these insights will be useful for development of anti-cancer and anti-viral drugs.

RIG-I inhibits pancreatic β cell proliferation through competitive binding of activated Src

Nutrition is a necessary condition for cell proliferation, including pancreatic β cells; however, over-nutrition, and the resulting obesity and glucolipotoxicity, is a risk factor for the development of Type 2 diabetes mellitus (DM), and causes inhibition of pancreatic β-cells proliferation and their loss of compensation for insulin resistance. Here, we showed that Retinoic acid (RA)-inducible gene I (RIG-I) responds to nutrient signals and induces loss of β cell mass through G1 cell cycle arrest. Risk factors for type 2 diabetes (e.g., glucolipotoxicity, TNF-α and LPS) activate Src in pancreatic β cells. Elevated RIG-I modulated the interaction of activated Src and STAT3 by competitive binding to STAT3. Elevated RIG-I downregulated the transcription of SKP2, and increased the stability and abundance of P27 protein in a STAT3-dependent manner, which was associated with inhibition of β cell growth elicited by Src. These results supported a role for RIG-I in β cell mass loss under conditions of metabolic surplus and suggested that RIG-I-induced blocking of Src/STAT3 signalling might be involved in G1 phase cycle arrest through the Skp2/P27 pathway in pancreatic β cells.