A novel ability of Smad3 to regulate proteasomal degradation of a Cas family member HEF1

Abstract

Smad3 is a key signal transducer of transforming growth factor-b (TGF-b) and activin, and is known to be a DNA-binding transcriptional regulator. Here we report a novel property of Smad3 in regulating the proteasomal degradation of the human enhancer of ®lamentation 1 (HEF1), which is a member of the Cas family of cytoplasmic docking proteins. Our studies revealed that Smad3 interacts with HEF1 and triggers the proteasomal degradation of HEF1 in overexpression systems. In addition, TGF-b stimulation induces rapid proteasomal degradation of endogenous HEF1 in different TGF-b-responsive cell lines. Interestingly, the degradation of HEF1 protein in epithelial cells is followed closely by an increase in HEF1 mRNA, resulting in a time-dependent increase in HEF1 protein level in TGF-b-treated cells. Furthermore, we observed that an elevated HEF1 protein level inhibits TGF-b-induced Smad3-mediated gene responses. These data provide the ®rst evidence for a novel cytoplasmic activity of Smad3 in regulating proteasomal degradation of HEF1 and also suggest a role for HEF1 in a negative feedback mechanism of the TGF-b signaling pathway.

Phosphorylation of human enhancer of filamentation (HEF1) on serine 369 induces its proteasomal degradation

“…5B). Recent published works agree with the preferential degradation of p115HEF1 isoform [16,18], although no kinase was identified yet. Interestingly, haematopoietic isoform of Cas/HEF1 Associated signal Transducer (CHAT-H), a binding partner of the Cas family proteins, is required to induce ser/thr phosphorylation of HEF1 and N-terminal domain of CHAT-H is necessary for this phosphorylation to occur [11].…”

“…Several reports demonstrated that ser/thr phosphorylation of HEF1 mediates its proteasomal degradation; p115HEF1 being the main isoform interacting with Smad3 and triggering the degradation of both proteins via an APC/CDH1 pathway [16,17]. Moreover AIP-4, an E3 ubiquitin ligase for HEF1, interacts more strongly with p115HEF1 than with the p105 isoform and ectopic expression of AIP-4 triggers preferentially p115HEF1 degradation [18].…”

“…HEF1 is also regulated by proteasomal degradation. In the TGFβ signalling pathway, HEF1 interacts with Smad3 and is consequently targeted to the proteasome through an APC/CDH1 dependent mechanism [16,17]. Alternatively, the Atrophin-1 Interacting Protein-4 (AIP-4) has been proposed as an ubiquitin E3 ligase in Smad3-HEF1 degradation induced by TGFβ [18].…”

“…Alternatively, the Atrophin-1 Interacting Protein-4 (AIP-4) has been proposed as an ubiquitin E3 ligase in Smad3-HEF1 degradation induced by TGFβ [18]. Different studies have reported that proteasomal degradation of HEF1 affects preferentially the serine/threonine phosphorylated form of HEF1 refered to as p115 [16,19].…”

Uncoupling of Promitogenic and Antiapoptotic Functions of IL-2 by Smad-Dependent TGF-β Signaling

“…Smads regulate gene expression by a variety of mechanisms, including recruitment of transcriptional coactivators such as CREB binding protein (CBP)/p300 (33-36) (37) as well as transcriptional corepressors, such as 5ЈTG3Ј interacting factor, Ski, and SnoN (38 -43). Recent studies have revealed that Smads can also regulate the stability of Smad nuclear interacting protein 1, a nuclear repressor of CBP/p300 (44,45), and the cytoplasmic signaling protein human enhancer of filamentation 1 (46).…”