Trypsin cleavage of the b1-adrenergic receptor

Jing Zhu, Susan F. Steinberg

Research output: Contribution to journalArticlepeer-review

Abstract

b1-Adrenergic receptors (b1ARs) are the principal mediators of catecholamine action in cardiomyocytes. We previously showed that b1ARs accumulate as both full-length and NH2-terminally truncated species in cells, that maturational processing of full-length b1ARs to an NH2-terminally truncated form is attributable to O-glycan-regulated proteolytic cleavage of the b1AR NH2-terminus at R31 ; L32 by ADAM17, and that NH2-terminally truncated b1ARs remain signaling competent but they acquire a distinct signaling phenotype. NH2-terminally truncated b1ARs differ from full-length b1ARs in their signaling bias to cAMP/PKA versus ERK pathways and only the NH2-terminally truncated form of the b1AR constitutively activates AKT and confers protection against doxorubicin-dependent apoptosis in cardiomyocytes. Since the R31 ; L32 sequence conforms to a trypsin consensus cleavage site, we used immunoblotting methods to test the hypothesis that b1ARs are also cleaved at R31 ; L32 by trypsin (an enzyme typically used to isolate cardiomyocytes from the intact ventricle). We show that full-length b1ARs are cleaved by trypsin and that trypsin cleaves the full-length b1AR NH2-terminus specifically at R31 ; L32 in CHO-Pro5 cells. Trypsin also cleaves b1ARs in cardiomyocytes, but at a second site that results in the formation of 40-kDa NH2-terminal and 30-kDa COOH-terminal fragments. The observation that cardiomyocyte b1ARs are cleaved by trypsin (a mechanism that constitutes a heretofore-unrecognized mechanism that would influence b1AR-signaling responses) suggests that studies that use standard trypsin-based procedures to isolate adult cardiomyocytes from the intact ventricle should be interpreted with caution. NEW & NOTEWORTHY Current concepts regarding the molecular basis for b1AR responses derive from literature predicated on the assumption that b1ARs signal exclusively as full-length receptor proteins. However, we recently showed that b1ARs accumulate as both full-length and NH2-terminally truncated forms. This manuscript provides novel evidence that b1-adrenergic receptors can be cleaved by trypsin and that cell surface b1AR cleavage constitutes a heretofore unrecognized mechanism to alter catecholamine-dependent signaling responses.

Original languageEnglish (US)
Pages (from-to)H486-H491
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume322
Issue number3
DOIs
StatePublished - Mar 2022
Externally publishedYes

Keywords

  • B -adrenergic receptors
  • Cardiomyocytes
  • Trypsin

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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