Regulation of the cdk inhibitor p27 and its deregulation in cancer

Chemopreventive effects of pterostilbene through p53 and cell cycle in mouse lung of squamous cell carcinoma model

Cell proliferation and cell death abnormalities are strongly linked to the development of cancer, including lung cancer. The purpose of this study was to investigate the effect of pterostilbene on cell proliferation and cell death via cell cycle arrest during the transition from G1 to S phase and the p53 pathway. A total of 24 female Balb/C mice were randomly categorized into four groups (n = 6): N-nitroso-tris-chloroethyl urea (NTCU) induced SCC of the lungs, vehicle control, low dose of 10 mg/kg PS + NTCU (PS10), and high dose of 50 mg/kg PS + NTCU (PS50). At week 26, all lungs were harvested for immunohistochemistry and Western blotting analysis. Ki-67 expression is significantly lower, while caspase-3 expression is significantly higher in PS10 and PS50 as compared to the NTCU (p < 0.05). There was a significant decrease in cyclin D1 and cyclin E2 protein expression in PS10 and PS50 when compared to the NTCU (p < 0.05). PS50 significantly increased p53, p21, and p27 protein expression when compared to NTCU (p < 0.05). Pterostilbene is a potential chemoprevention agent for lung SCC as it has the ability to upregulate the p53/p21 pathway, causing cell cycle arrest.

The non-canonical functions of p27(Kip1) in normal and tumor biology

p27(Kip1) was first discovered as a key regulator of cell proliferation. The canonical function of p27(Kip1) is inhibition of cyclin-dependent kinase (CDK) activity. In addition to its initial identification as a CDK inhibitor, p27(Kip1) has also emerged as an intrinsically unstructured, multifunctional protein with numerous non-canonical, CDK-independent functions that exert influence on key processes such as cell cycle regulation, cytoskeletal dynamics and cellular plasticity, cell migration, and stem-cell proliferation and differentiation. Many of these non-canonical functions, depending on the cell-specific contexts such as oncogenic activation of signaling pathways, have the ability to turn pro-oncogenic in nature and even contribute to tumor-aggressiveness and metastasis. This review discusses the various non-canonical, CDK-independent mechanisms by which p27(Kip1) functions either as a tumor-suppressor or tumor-promoter.

Bone marrow mesenchymal stem cells modulate the expression of RhoA and P27 in hepatic stellate cells

AIM: To investigate the effects of bone marrow mesenchymal stem cells (MSCs) on the mRNA and protein expression of RhoA (Ras homolog gene family member A) and P27 in hepatic stellate cells (HSCs) and explore the mechanisms how MSCs regulate cell cycle progression of HSCs.

METHODS: MSCs were isolated from rat bone marrow and propagated in culture flasks. Meanwhile, HSCs and fibroblasts were thawed and passaged. An indirect co-culture system between MSCs/fibroblasts and HSCs was established using a Transwell membrane system (diameter: 24 mm; pore size: 0.4 μm). HSCs were randomly divided into three groups: blank control group (HSCs alone), negative control group (HSCs plus fibroblasts), and experimental group (HSCs plus MSCs). Cell proliferation was tested by WST-8 assay. Cell-cycle phases were determined by flow cytometry. The mRNA and protein expression of RhoA and P27 in HSCs was determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively.

RESULTS: After 24 h of co-culture, the reduced rate of cell proliferation in the experimental group was significantly higher than those in the blank control group and negative control group co-culture(both P < 0.01). Flow cytometry analysis showed that, after 12 hours of co-culture, the percentage of HSCs in the G₀/G₁ phase in the experimental group was significantly higher than those in the two control groups (both P < 0.01), while the percentage of HSCs in the S phase in the experimental group was significantly lower than those in the two control groups (both P < 0.01). After 12 h of co-culture, the expression level of RhoA mRNA in the experimental group was significantly lower than those in the two control groups (both P < 0.01), whereas the expression level of P27 mRNA showed no significant differences between the experimental group and the two control groups (both P > 0.05). The expression level of RhoA protein in the experimental group was significantly lower than those in the two control groups (both P < 0.01), whereas the expression level of P27 in the experimental group was significantly higher than those in the two control groups (both P < 0.01). No correlation was noted between the expression of RhoA and P27 mRNAs (r = 0.105). However, a negative correlation was noted between the expression of RhoA and P27 proteins (r = -0.943, P < 0.01).

CONCLUSION: MSCs inhibit the proliferation of HSCs possibly by modulating the RhoA-P27 pathway to alter cell cycle progression of HSCs. The upregulation of P27 protein may be due to the downregulation of RhoA activity.