Abstract 3022: GPR109A activation limits cell growth by inducing p53 and its targets in human colon cancer cells
Authors: Thangaraju Muthusamy , Thangaraju Nanditi N. , Gilstrap Lauren , Chimenti Madison , Patel Tulshi , Sivaprakasam Sathish , Patel Nikhil , Manicassamy Santhakumar , Prasad Puttur D. , Ganapathy Vadivel 
Published: March 2024

Abstract
Chemical carcinogens or xenobiotics present in the diet play a significant role in colon cancer (CC) formation. p53, a tumor suppressor and multi-functional protein, provides an important barrier against the initiation and maintenance of CC. p53 mutation or inactivation is observed in about 60% of CCs and about 90% of all cancers. Therefore, therapeutic avenues that will rejuvenate wild-type p53 or target mutant p53 should have a significant impact on the prevention and treatment of CC. GPR109A, a G-protein coupled receptor for the FDA-approved lipid-lowering drug Niacin (NA), bacterial metabolite Butyrate (BTR), and ketone body β-hydroxybutyrate (BHB), functions as a novel tumor suppressor in the colon by providing the molecular link between colonic bacteria and p53 function. GPR109A activation limits cAMP by inhibiting adenylate cyclase (AC), which induces RAS and its downstream growth-promoting signaling. cAMP also enhances the binding of MDM2 to p53 and induces the proteasomal degradation of p53. p53 is an NAD+-dependent molecule and deficiency of NA, the precursor of NAD+, impairs p53 function. We tested the role of GPR109A and its agonists (NA, BTR, and BHB) in normal immortalized colon epithelial cell lines (CCD33 and CCD81) and various CC lines such as HCT116-p53+/+, HCT116-p53−/−, DLD1 (p53 point mutation), VACO4A (p53 insertion mutation), and SW498 (p53 deletion) and measured cell proliferation, cell cycle, apoptosis, and analyzed the expression of GPR109A and p53 (total, phosphorylated, and acetylated), MDM2, p21, Bax, and Puma in the presence and absence of GPR109109 agonists. We found that GPR109A expression is significantly reduced in CC cell lines, especially in p53 mutant cell lines, when compared to normal immortalized colonic epithelial cell lines. Treatment of CC cell lines with GPR109A agonists-induced apoptosis in wild-type p53 expressing CC by activating p53 and its targets. However, some lesser extent in p53 mutant or p53 null cell lines. Lentiviral-mediated GPR109A expression in CC cell lines itself induced apoptosis in both wild-type and mutant p53 expressing CC cell lines and GPR109A agonists treatment induced further. Interestingly, GPR109A agonists BTR and BHB significantly increased apoptosis in p53 mutant and p53 null CC cell lines in a p53-independent manner. Overall, our results provide evidence that GPR109A activation can be used as an effective therapeutic strategy for the treatment of CC.
Citation Format: Muthusamy Thangaraju, Nanditi N. Thangaraju, Lauren Gilstrap, Madison Chimenti, Tulshi Patel, Sathish Sivaprakasam, Nikhil Patel, Santhakumar Manicassamy, Puttur D. Prasad, Vadivel Ganapathy. GPR109A activation limits cell growth by inducing p53 and its targets in human colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3022.