The cardiac translational landscape reveals that micropeptides are new players involved in cardiomyocyte hypertrophy.

Hypertrophic growth of cardiomyocytes is one of the major compensatory responses in the heart after physiological or pathological stimulation. Protein synthesis enhancement, which is mediated by the translation of messenger RNAs, is one of the main features of cardiomyocyte hypertrophy. Although the transcriptome shift caused by cardiac hypertrophy induced by different stimuli has been extensively investigated, translatome dynamics in this cellular process has been less studied. Here, we generated a nucleotide-resolution translatome as well as transcriptome data from isolated primary cardiomyocytes undergoing hypertrophy. More than 10,000 open reading frames (ORFs) were detected from the deep sequencing of ribosome-protected fragments (Ribo-seq), which orchestrated the shift of the translatome in hypertrophied cardiomyocytes. Our data suggest that rather than increase the translational rate of ribosomes, the increased efficiency of protein synthesis in cardiomyocyte hypertrophy was attributable to an increased quantity of ribosomes. In addition, more than 100 uncharacterized short ORFs (sORFs) were detected in long noncoding RNA genes from Ribo-seq with potential of micropeptide coding. In a random test of 15 candidates, the coding potential of 11 sORFs was experimentally supported. Three micropeptides were identified to regulate cardiomyocyte hypertrophy by modulating the activities of oxidative phosphorylation, the calcium signaling pathway, and the mitogen-activated protein kinase (MAPK) pathway. Our study provides a genome-wide overview of the translational controls behind cardiomyocyte hypertrophy and demonstrates an unrecognized role of micropeptides in cardiomyocyte biology.

G protein-coupled receptor GPR68 inhibits lymphocyte infiltration and contributes to gender-dependent melanoma growth.

Introduction: Melanoma is a common and aggressive type of skin cancer with rising incidence rate globally. Gender is one of the determining factors, and overall males have a higher risk of developing melanoma as well as worse prognosis. Emerging evidence show that GPR68, a G protein-coupled receptor that is sensitive to acid and mechanical stimulations for cellular microenvironment, plays an important role in tumor biology. However, whether GPR68 is involved in gender-dependent regulation of tumor growth is unclear. Methods: We established a syngeneic melanoma model in Gpr68-deficient mice and investigated tumor growth in males and females. The GPR68 activation-induced cellular responses of melanocytes, including intracellular calcium dynamics, proliferation and migration were measured. The landscape of tumor-infiltrating immune cells were analyzed by flow cytometry and the expression various cytokines were checked by qRT-PCR. Results: GPR68 is required for melanoma growth in males but dispensable in females. GPR68 is expressed and functional in B16-F10 melanocytes, but the activity of the receptor does not directly contribute to proliferation and migration of the cells. GPR68 inhibits infiltration of CD45+ lymphocytes, CD8+ T cells and NK cells in melanoma in male mice, but has no apparent effect in females. Furthermore, GPR68 functionally inhibits the expression of IFNγ in the tumor infiltrating CD8+ T cells and NK cells as well as the inflammatory cytokine expression in the spleen in male mice but not in females. Our results show the gender-dependent modulatory effect of GPR68 on tumor-infiltrating immune cells and their tumor-killing capacity. Discussion: GPR68 is sensor for acid and mechanical stimulations, which are two important factors in the microenvironment associated with tumor growth and metastasis. Our results suggest a prominent role of the receptor molecules in tumor biology in a gender-dependent manner. Since GPCRs are more feasible to develop small molecule drugs compared to transcription factors, our study demonstrates the potential of GPR68 as a novel druggable therapeutic target for melanoma in male patients.