Cancer prevention by retinoids and carotenoids: independent action on a common target

Area of Science:

• Molecular Biology
• Cancer Research
• Cellular Communication

Background:

• Human tumors often exhibit deficient gap junctional communication (GJC).
• Restoring GJC via connexin expression can reduce neoplastic growth.
• Cancer-preventive retinoids and carotenoids upregulate connexin 43 (Cx43) expression, but the mechanism is unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which retinoids and carotenoids upregulate Cx43 expression.
• To investigate the role of retinoic acid receptor (RAR) and peroxisome proliferator-activated receptor gamma (PPAR-gamma) in Cx43 gene regulation.
• To identify the specific DNA regions involved in the transcriptional activation of Cx43.

Main Methods:

• Utilized cell culture models (10T1/2 and F9 cells) with Cx43 luciferase reporter constructs.
• Employed specific antagonists for RAR (Ro 41-5253) and PPAR-gamma (GW9662).
• Performed mRNA stability assays and site-directed mutagenesis of the Cx43 promoter region.

Main Results:

• Retinoid-induced Cx43 expression was RAR-dependent, while astaxanthin-induced expression was PPAR-gamma-dependent.
• Cx43 mRNA induction occurred via direct transcriptional activation, independent of protein synthesis.
• A specific GC-box within the -158 bp to +209 bp promoter region was critical for retinoid responsiveness.
• Combined treatment with retinoids and carotenoids resulted in supra-additive Cx43 expression.

Conclusions:

• Retinoids and carotenoids employ distinct molecular pathways to transcriptionally activate Cx43 gene expression.
• Understanding these separate mechanisms offers potential for targeted cancer prevention strategies.
• Cx43 upregulation is a key event in the anti-cancer effects of these compounds.