TIMP3 Modulates GHR Abundance and GH Sensitivity.

Area of Science:

• Biochemistry
• Cell Biology
• Endocrinology

Background:

• Growth hormone receptor (GHR) mediates crucial anabolic and metabolic functions via cell surface binding and intracellular signaling.
• Cell surface GHR levels dynamically regulate GH signaling, with metalloprotease-mediated cleavage playing a key role in GHR abundance.
• The TNF-α converting enzyme (TACE; ADAM17) proteolytically cleaves GHR, and Tissue inhibitors of metalloproteases-3 (TIMP3) is a known inhibitor of TACE.

Purpose of the Study:

• To investigate the interplay between cellular TACE, TIMP3 expression, GHR metalloproteolysis, and GH sensitivity.
• To elucidate the mechanisms by which TIMP3 modulates TACE activity and GHR abundance.

Main Methods:

• Utilized two distinct model cell lines with varying sensitivities to inducible GHR proteolysis.
• Assessed cellular levels of mature TACE, unprocessed TACE precursor, and TIMP3.
• Correlated these molecular levels with GHR proteolysis rates and GH-induced signaling.

Main Results:

• Cell lines showed differential sensitivity to inducible GHR proteolysis, directly correlating with mature TACE levels and inversely with TIMP3 levels.
• TIMP3 was implicated as a key modulator of cell surface GHR abundance and GH-mediated cellular signaling.
• TIMP3 influences both TACE activity and TACE maturation, affecting the availability of the active enzyme form.

Conclusions:

• TIMP3 plays a significant role in regulating GHR levels and GH sensitivity through its inhibition of TACE.
• Both endogenous and exogenous TIMP3 can modulate GHR abundance and GH signaling pathways.
• TIMP3's regulatory effects extend to TACE maturation, impacting the overall GHR proteolysis cascade.