Regulation of Cystic Fibrosis Transmembrane Regulator Trafficking and Protein Expression by a Rho Family Small GTPase TC10

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR)-interacting protein, CFTR-associated ligand (CAL) down-regulates total and cell surface CFTR by targeting CFTR for degradation in the lysosome. Here, we report that a Rho family small GTPase TC10 interacts with CAL. This interaction specifically up-regulates CFTR protein expression. Co-expression of the constitutively active form, TC10Q75L, increases total and cell surface CFTR in a dose-dependent fashion. Moreover, co-expression of the dominant-negative mutant TC10T31N causes a dose-dependent reduction in mature CFTR. The effect of TC10 is independent of the level of CFTR expression, because a similar effect was observed in a stable cell line that expresses one-tenth of CFTR. Co-expression of TC10Q75L did not have a similar effect on the expression of plasma membrane proteins such as Frizzled-3 and Pr-cadherin or cytosolic proteins such as tubulin and green fluorescent protein. TC10Q75L also did not have a similar effect on the vesicular stomatitis virus glycoprotein. Co-expression of constitutively active and dominant-negative forms of Cdc42 or RhoA did not affect CFTR expression in a manner similar to TC10, indicating that the effect of TC10 is unique within the Rho family. Metabolic pulse-chase experiments show that TC10 did not affect CFTR maturation, suggesting that it exerts its effects on the mature CFTR. Importantly, TC10Q75L reverses CAL-mediated CFTR degradation, suggesting that TC10Q75L inhibits CAL-mediated degradation of CFTR. TC10Q75L does not operate by reducing CAL protein expression or its ability to form dimers or interact with CFTR. Interestingly, the expression of TC10Q75L causes a dramatic redistribution of CAL from the juxtanuclear region to the plasma membrane where the two molecules overlap. These data suggest that TC10 regulates both total and plasma membrane CFTR expression by interacting with CAL. The GTP-bound form of TC10 directs the trafficking of CFTR from the juxtanuclear region to the secretory pathway toward the plasma membrane, away from CAL-mediated degradation of CFTR in the lysosome.

Isoform-specific Interaction of Golgin-160 with the Golgi-associated Protein PIST

“…This same region of PIST has been reported to mediate interactions with TC10, a Rho GTPase, (20) and syntaxin-6, a Q-SNARE (23). Recently, exogenous expression of TC10 has been proposed to regulate cystic fibrosis transmembrane conductance receptor trafficking and expression through its interaction with PIST (34). Therefore, binding of golgin-160, TC10, and syntaxin-6 to PIST may coordinate membrane trafficking of some plasma membrane proteins in cell types where these proteins are expressed.…”

Targeting CAL as a Negative Regulator of ΔF508-CFTR Cell-Surface Expression

“…In the case of CFTR, the effect is mediated by reductions in the rate of membrane insertion and in the half-life of the channels at the cell surface (21), and can be prevented by blocking endocytosis or lysosomal degradation (25). The negative effect of CAL overexpression on CFTR expression levels can also be reversed by the simultaneous overexpression of NHERF1, which competes for the C-terminal TRL binding motif (21), or by overexpression of TC10, a Rho GTPase whose constitutively active form redistributes CAL intracellularly toward the plasma membrane (26).…”

Membrane Organization and Dynamics in Cell Polarity

“…Later studies showed that TC10 activity is coupled to vesicle fusion at the plasma membrane (Cheng et al 2005;Kawase et al 2006). Together, a conserved function of Cdc42/TC10 family proteins in exocytosis seems to be emerging.…”