Transforming Growth Factor β Regulates the Expression of the M2 Muscarinic Receptor in Atrial Myocytes via an Effect on RhoA and p190RhoGAP

Transforming growth factor β (TGFβ) signaling is involved in the development and regulation of multiple organ systems and cellular signaling pathways. We recently demonstrated that TGFβ regulates the response of atrial myocytes to parasympathetic stimulation. Here, TGFβ1 is shown to inhibit expression of the M2 muscarinic receptor (M2), which plays a critical role in the parasympathetic response of the heart. This effect is mimicked by overexpression of a dominant negative mutant of RhoA and by the RhoA kinase inhibitor Y27632, whereas adenoviral expression of a dominant activating-RhoA reverses TGFβ inhibition of M2 expression. TGFβ1 also mediates a decrease in GTP-bound RhoA and a reciprocal increase in the expression of the RhoA GTPase-activating protein, p190RhoGAP, whereas total RhoA is unchanged. Inhibition of M2 promoter activity by TGFβ1 is mimicked by overexpression of p190RhoGAP, whereas a dominant negative mutant of p190RhoGAP reverses this effect of TGFβ1. In contrast to atrial myocytes, in mink lung epithelial cells, in which TGFβ signaling through activation of RhoA has been previously identified, TGFβ1 stimulated an increase in GTP-bound RhoA in association with a reciprocal decrease in the expression of p190RhoGAP. Both effects demonstrated a similar dose dependence on TGFβ1. Thus TGFβ regulation of M2 muscarinic receptor expression is dependent on RhoA, and TGFβ regulation of p190RhoGAP expression may be a cell type-specific mechanism for TGFβ signaling through RhoA.