A novel function of the monomeric CCT epsilon subunit connects the serum response factor pathway to chaperone-mediated actin folding

• Correct protein folding is fundamental for maintaining protein homeostasis and avoiding the formation of potentially cytotoxic protein aggregates. Although some proteins appear to fold unaided, actin requires assistance from the oligomeric molecular chaperone CCT. Here we report an additional connection between CCT and actin by identifying one of the CCT subunits, CCT epsilon, as a component of the myocardin-related cotranscription factor-A (MRTF-A)/serum response factor (SRF) pathway. The SRF pathway registers changes in G-actin levels, leading to the transcriptional up-regulation of a large number of genes after actin polymerization. These genes encode numerous actin-binding proteins as well as actin. We show that depletion of the CCT epsilon subunit by siRNA enhances SRF signaling in cultured mammalian cells by an actin assembly-independent mechanism. Overexpression of CCTe in its monomeric form revealed that CCT epsilon binds via its substrate-binding domain to the C-terminal region of MRTF-A and that CCT epsilon is able to alter the nuclear accumulation of MRTF-A after stimulation by serum addition. Given that the levels of monomeric CCT epsilon conversely reflect the levels of CCT oligomer, our results suggest that CCT epsilon provides a connection between the actin-folding capacity of the cell and actin expression.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine (hsv//eng)

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

CYTOSOLIC CHAPERONIN

SUBSTRATE-BINDING

TUBULIN

COMPLEX

COACTIVATOR

GELSOLIN

DOMAIN

CELLS

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