CDK2/4 regulate retinoic acid-induced G1 arrest in hepatocellular carcinoma cells
Hae-Yun Jung1, Sun-Hee Park, Young Do Yoo
1Genomic Research Center for Lung and Breast/Ovarian Cancer, Korea University College of Medicine, Seoul, Republic of Korea.
Abstract:
Retinoic acid (RA) is an important regulator of normal cellular proliferation and differentiation and suppressor of tumor growth by cell cycle arrest and apoptosis. Furthermore, RA showed a chemo-preventive activity in preclinical and/or clinical models of lung, head and neck, breast, and hepatocellular carcinoma (HCC). In this study, we examined the effect of RA on the proliferation of human HCC cells, in order to analyze its mode of action and, finally, we attempted to find a surrogate biomarker of RA for HCC chemopreventive treatment. Our findings suggested that the growth inhibition of RA in HCC cells differed according to G(1) phase delay by CDK2 or 4, finally induction of apoptosis. No correlation was found between RA sensitivity and the expression of nuclear retinoid receptors, such as RARs or RXRs in HCC cells. RA treatment caused cell cycle arrest at G(1) and decreased the expressions and activities of CDK2 or CDK4 in RA-sensitive HepG2 and SNU354 cells. On the other hand, RA-resistant Hep3B and SNU449 cells progressed into the S/G(2)+M phase and showed increased CDK2 and CDK4 expression and activity. Since the inhibition of CDK2 or 4 activities resulted in sensitization of HCC cells to RA, the combination of RA and compounds of inhibiting CDKs such as UCN01 and flavopiridol might be a useful targeted therapy strategy for HCC.
Insights
Retinoic acid (RA) inhibits hepatocellular carcinoma (HCC) cell growth by delaying the cell cycle and inducing apoptosis. Targeting cyclin-dependent kinases (CDKs) alongside RA may offer a novel HCC therapy.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Retinoic acid (RA) is a crucial regulator of cell proliferation, differentiation, and apoptosis.
- RA exhibits chemopreventive properties against various cancers, including hepatocellular carcinoma (HCC).
Purpose of the Study:
- To investigate the effect of RA on human HCC cell proliferation.
- To elucidate the mechanism of action of RA in HCC.
- To identify potential biomarkers for RA's chemopreventive efficacy in HCC.
Main Methods:
- Assessing RA's impact on HCC cell cycle progression (G1, S, G2/M phases).
- Measuring the expression and activity of key cell cycle regulators, specifically CDK2 and CDK4.
- Evaluating the correlation between RA sensitivity and nuclear retinoid receptor (RARs, RXRs) expression.
Main Results:
- RA induced G1 cell cycle arrest and reduced CDK2/CDK4 expression/activity in sensitive HCC cells (HepG2, SNU354).
- RA-resistant HCC cells (Hep3B, SNU449) showed progression into S/G2+M phases with increased CDK2/CDK4 activity.
- No correlation was observed between RA sensitivity and RAR/RXR expression levels.
Conclusions:
- RA's growth inhibition in HCC is mediated by G1 phase delay via CDK2/4 modulation, leading to apoptosis.
- Inhibiting CDK2/4 activity sensitizes HCC cells to RA, suggesting a potential combination therapy strategy.
- Targeting CDK activity alongside RA presents a promising therapeutic approach for HCC.
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