Abstract
Alternative splicing of G protein-coupled receptors has been observed, but their functions are largely unknown. Here, we report that a splice variant (SV1) of the human growth hormone releasing hormone receptor (GHRHR) is capable of transducing biased signal. Differing only at the receptor N terminus, GHRHR predominantly activates Gs while SV1 selectively couples to β-arrestins. Based on the cryo-electron microscopy structures of SV1 in the apo state or in complex with the Gs protein, molecular dynamics simulations reveal that the N termini of GHRHR and SV1 differentiate the downstream signaling pathways, Gs vs. β-arrestins. Suggested by mutagenesis and functional studies, it appears that GHRH-elicited signal bias towards β-arrestin recruitment is constitutively mediated by SV1. The level of SV1 expression in prostate cancer cells is also positively correlated with ERK1/2 phosphorylation but negatively correlated with cAMP response. Our findings imply that constitutive signal bias may be a mechanism that ensures cancer cell proliferation.
Significance Statement The mechanism of functional changes induced by alternative splicing of GHRHR is largely unknown. Here, we demonstrate that GHRH-elicited signal bias towards β-arrestin recruitment is constitutively mediated by SV1. The cryo-electron microscopy structures of SV1 and molecular dynamics simulations reveal the different functionalities between GHRHR and SV1 at the near-atomic level, i.e., the N termini of GHRHR and SV1 differentiate the downstream signaling pathways, Gs vs. β-arrestins. Our findings provide valuable insights into functional diversity of class B1 GPCRs which may aid in the design of better therapeutic agents against certain cancers.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Competing Interest Statement: The authors declare no competing interests.