RhoA/C inhibits proliferation by inducing the synthesis of GPRC5A

The dark sides of the GPCR tree - research progress on understudied GPCRs

A large portion of the human GPCRome is still in the dark and understudied, consisting even of entire subfamilies of GPCRs such as odorant receptors, class A and C orphans, adhesion GPCRs, Frizzleds and taste receptors. However, it is undeniable that these GPCRs bring an untapped therapeutic potential that should be explored further. Open questions on these GPCRs span diverse topics such as deorphanisation, the development of tool compounds and tools for studying these GPCRs, as well as understanding basic signalling mechanisms. This review gives an overview of the current state of knowledge for each of the diverse subfamilies of understudied receptors regarding their physiological relevance, molecular mechanisms, endogenous ligands and pharmacological tools. Furthermore, it identifies some of the largest knowledge gaps that should be addressed in the foreseeable future and lists some general strategies that might be helpful in this process.

The G protein-coupled receptor GPRC5A-a phorbol ester and retinoic acid-induced orphan receptor with roles in cancer, inflammation, and immunity

GPRC5A is the first member of a new class of orphan receptors coupled to G proteins, which also includes GPRC5B, GPRC5C, and GPRC5D. Since its cloning and identification in the 1990s, substantial progress has been made in understanding the possible functions of this receptor. GPRC5A has been implicated in a variety of cellular events, such as cytoskeleton reorganization, cell proliferation, cell cycle regulation, migration, and survival. It appears to be a central player in different pathological processes, including tumorigenesis, inflammation, immune response, and tissue damage. The levels of GPRC5A expression differ depending on the type of cancer, with increased expression in colon, pancreas, and prostate cancers; decreased expression in lung cancer; and varied results in breast cancer. In this review, we discuss the early discovery of GPRC5A as a phorbol ester-induced gene and later as a retinoic acid-induced gene, its regulation, and its participation in important canonical pathways related to numerous types of tumors and inflammatory processes. GPRC5A represents a potential new target for cancer, inflammation, and immunity therapies.

DNA methyltransferase 1 inhibits microRNA-497 and elevates GPRC5A expression to promote chemotherapy resistance and metastasis in breast cancer

Background

Abnormal DNA methylation of tumor suppressor gene promoter has been found in breast cancer. Therefore, the current study set out to explore how DNA methyltransferase 1 (DNMT1) affects breast cancer through mediating miR-497/GPRC5A axis.

Methods

After loss and gain-of-function approaches were conducted in MCF-7/ADR and MCF-7 cells, cell viability, IC50 value, invasion, migration and apoptosis were measured, respectively. In addition, drug resistance, metastasis and apoptosis-related protein expression were examined using immunoblotting. ChIP and dual-luciferase reporter gene assays were carried out to validate relationship among DNMT1, miR-497, and GPRC5RA. Subcutaneous xenograft tumor model in nude mice was established to detect effects of DNMT1 on growth and metastasis of breast cancer in vivo.

Results

It was found that DNMT1 was notably increased, while miR-497 was poorly-expressed in breast cancer. Highly-expressed DNMT1 could promote chemotherapy resistance and metastasis of breast cancer. Meanwhile, DNMT1 modified methylation of CpG island in miR-497 promoter region, thereby repressing miR-497 level. In addition, miR-497 targeted GPRC5A expression to curb chemotherapy resistance and metastasis of breast cancer cells. Lastly, in vivo experiments showed that knockdown of DNMT1 could suppress breast cancer growth and metastasis.

Conclusions

Collectively, our findings indicated that DNMT1 may inhibit miR-497 and boost the expression of GPRC5A through methylation, thus augmenting breast cancer chemotherapy resistance and metastasis, which provides novel mechanistic insight into the unrecognized roles of DNMT1 in breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02466-5.

Report of the 24th Meeting on Signal Transduction 2021

The annual meeting “Signal Transduction—Receptors, Mediators and Genes” of the Signal Transduction Society (STS) is an interdisciplinary conference which is open to all scientists sharing a common interest in the elucidation of the signaling pathways mediating physiological or pathological processes in the health and disease of humans, animals, plants, fungi, prokaryotes, and protists. The 24th meeting on signal transduction was held from 15 to 17 November 2021 in Weimar, Germany. As usual, keynote presentations by invited scientists introduced the respective workshops, and were followed by speakers chosen from the submitted abstracts. A special workshop focused on “Target Identification and Interaction”. Ample time was reserved for the discussion of the presented data during the workshops. Unfortunately, due to restrictions owing to the SARS-CoV-2 pandemic, the poster sessions—and thus intensive scientific discussions at the posters—were not possible. In this report, we provide a concise summary of the various workshops and further aspects of the scientific program.

Overexpression of RhoV Promotes the Progression and EGFR-TKI Resistance of Lung Adenocarcinoma

Background

The Rho GTPase family with ~20 member genes play central roles in a wide variety of cellular processes and tumor cell migration and metastasis. Different Rho GTPase may play different roles in the progression of lung adenocarcinoma.

Methods

We comprehensively examined the expression of all Rho GTPase family member genes in a panel of lung adenocarcinoma patient’s tumors and matched normal tissues. We next investigated the critical role of RhoV in different lung adenocarcinoma cells and animal models.

Results

RhoV was identified as one of the most significantly overexpressed Rho GTPases in lung adenocarcinoma and associated with patients’ survival. Silencing RhoV expression inhibits proliferation, migration and invasion, and tumorigenicity capacities of lung adenocarcinoma cells. Moreover, knockdown RhoV promoted the sensitivity of EGFR-TKI in the gefitinib resistant PC9 cells (PC9-GR) and aggravated gefitinib-induced lung cancer cell apoptosis both in PC9 and PC9-GR cells. Our data also indicated that RhoV induced progression and EGFR-TKI resistance of lung adenocarcinoma may be related to the activation of the AKT/ERK pathway.

Conclusion

Overexpression of RhoV in lung adenocarcinoma promotes the progression and EGFR-TKI resistance, suggesting RhoV is a promising prognosis and therapeutic target of lung adenocarcinoma.

GPRC5A Is a Negative Regulator of the Pro-Survival PI3K/Akt Signaling Pathway in Triple-Negative Breast Cancer

Breast cancer is one of the most common types of malignancy worldwide; however, its underlying mechanisms remain unclear. In the present study, we investigated the roles of G-protein-coupled receptor family C, member 5, group A (GPRC5A) in cell apoptosis in triple-negative breast cancer (TNBC). The expression of GPRC5A in breast cancer cell lines was detected by real time PCR and western blot. And the results suggested that GPRC5A was downregulated in breast cancer cell lines compared to normal breast epithelial cell lines. Additionally, the expression of GPRC5A in TCGA database was analyzed in silico. GPRC5A exhibited the lowest expression levels in TNBC compared to ER⁺ and HER2⁺ breast cancer. Overexpression of GPRC5A in MDA-MB-231 and MDA-MB-468 cells promoted apoptosis, whereas depletion of GPRC5A in T47D and MCF7 cells inhibited cell apoptosis via the intrinsic apoptotic pathway. We performed RNA-sequencing in GPRC5A overexpressed MDA-MB-231 and the control cells. The results facilitated the identification of a number of signaling pathways involved in this process, and the PI3K/Akt signaling pathway was found to be one the most important. A specific activator of the PI3K/Akt signaling pathway inhibited apoptosis of breast cancer cells, whereas cotreatment of this activator with a GPRC5A-expressing plasmid reduced this effect. Similarly, a specific inhibitor of the PI3K/Akt signaling pathway increased cell apoptosis by activating caspase-3 and caspase-9, whereas co-incubation of the inhibitor with a short hairpin RNA targeting GPRC5A significantly reduced the cell apoptotic rate. Additionally, the overexpression of GPRC5A suppressed tumor growth by inducing cell apoptosis in vivo. Taken together, the present study identified GPRC5A as a protective factor against the progression of human triple-negative breast cancer by increasing cell apoptosis via the regulation of the PI3K/Akt signaling pathway.

GPRC5A: An emerging prognostic biomarker for predicting malignancy of Pancreatic Cancer based on bioinformatics analysis

Background: Pancreatic cancer (PaCa) is a highly lethal malignancy. The treatment options for PaCa lack efficacy. The study aimed to explore the molecular biomarkers for predicting survival of PaCa and identify the potential carcinogenic mechanisms of the selected gene. Methods: Based on public databases of PaCa, differentially expressed genes (DEGs) were identified using Networkanalyst. Survival analyses were exerted on GEPIA. Oncomine and The Human Protein Atlas were used for verifying the expression on mRNA and protein levels. Enrichment analyses were generated on Metascape and gene set enrichment analysis (GSEA). Univariate analyses were performed to determine the clinical factors associated with the expression of GPRC5A. Results: GPRC5A was identified as the most valuable gene in predicting survival of PaCa patients. Patients with high expression of GPRC5A showed larger tumor size, higher TNM stages, higher tumor grade, and more positive resection margin. In mutant KRAS, TP53, CDKN2A and SMAD4 group, the expression of GPRC5A was higher than non-mutant group. Mechanistically, GPRC5A may promote metastasis of PaCa mainly via regulating epithelial-mesenchymal transition (EMT) and neuroactive ligand-receptor interaction. Conclusion: GPRC5A may act as an oncogene in the progression of PaCa and could be a prognostic biomarker in predicting survival of PaCa.