Vascular smooth muscle RbFox2 regulates the cytoskeleton and arterial stiffness by a RhoBTB1-Cullin-3 mechanism

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Abstract

The RhoBTB1-Cullin3 (CUL3) pathway in smooth muscle cells (SMCs) controls the ubiquitination and proteasomal degradation of target proteins that regulate vasodilation, vasoconstriction, and the actin cytoskeleton, and through this blood pressure (BP) and arterial stiffness. Using proximity labelling coupled with mass spectrometry in A7R5 SMCs, we identified proteins which bound to the C-terminal half of RhoBTB1 which functions as an adapter to deliver substrates to CUL3. We examined the physiological relevance of one of these substrates, RbFox2. Co-immunoprecipitation validated the interaction of RbFox2 with RhoBTB1. RbFox2 expression was elevated in response to inhibition of the ubiquitination-proteasomal pathway, CUL3-deficiency, and RhoBTB1 inhibition by either siRNA or angiotensin II (ANG). RbFox2 was ubiquitinated in a RhoBTB1- and CUL3-dependent manner suggesting its regulation through the RhoBTB1-CUL3-dependent ubiquitin-proteasome pathway. Inhibition of RbFox2 impaired the actin cytoskeleton in A7R5 cells and in primary SMC from RbFox2Flox/Flox (RbFox2F/F) mice and decreased the levels of globular and filamentous actin. ANG increased BP and arterial stiffness of RbFox2F/F mice, but the progression of arterial stiffness was halted after SMC-specific RbFox2 deletion despite a continued rise in BP. We conclude that RhoBTB1 and RbFox2 are important regulators of arterial stiffness through a mechanism that influences cytoskeletal integrity.

Authors

Gaurav Kumar, Nisita Chaihongsa, Daniel T. Brozoski, Daria Golosova, Ibrahim Vazirabad, Ko-Ting Lu, Kelsey K. Wackman, Ravi K. Singh, Curt D. Sigmund