Crk-associated substrate lymphocyte type regulates transforming growth factor-β signaling by inhibiting Smad6 and Smad7

Abstract

Crk-associated substrate lymphocyte type (Cas-L) is a 105 kDa docking protein with diverse functional properties, including regulation of cell division, proliferation, migration and adhesion. Cas-L is also involved in b1 integrin-or antigen receptor-mediated signaling in B and T cells. In the present study, we demonstrate that Cas-L potentiates transforming growth factor-b (TGF-b) signaling pathway by interacting with Smad6 and Smad7. Immunoprecipitation experiments reveal that single domain deletion of full-length Cas-L completely abolishes its docking function with Smad6 and Smad7, suggesting that the natural structure of Cas-L is necessary for its association with Smad6 and Smad7. On the other hand, both N-terminal and C-terminal deletion mutants of Smad6 and Smad7 still retain their docking ability to Cas-L, suggesting that Smad6 and Smad7 possess several binding motifs to Cas-L. Moreover, Cas-L interaction with Mad-homology (MH)2 domain, but not with MH1 domain of Smad6 or Smad7, ameliorates TGF-b-induced signaling pathway. Finally, depletion of Cas-L by smallinterfering RNA oligo attenuates TGF-b-induced growth inhibition of Huh-7 cells, with a concomitant reduction in phosphorylation of Smad2 and Smad3. These results strongly suggest that Cas-L is a potential regulator of TGF-b signaling pathway. Oncogene (2007) 26, 893-904.

Molecular basis for HEF1/NEDD9/Cas-L action as a multifunctional co-ordinator of invasion, apoptosis and cell cycle

“…These interactions can cause proteolysis of HEF1/ NEDD9/Cas-L [28]. Reciprocally, HEF1/NEDD9/Cas-L can modulate the activity of the SMAD proteins, limiting TGF-b signaling output [51]. This intimate connection between TGF-b and HEF1/NEDD9/Cas-L may prove to be important for the action of HEF1/NEDD9/Cas-L in metastasis.…”

“…Several groups have demonstrated direct interaction of HEF1/NEDD9/Cas-L with SMAD proteins, ubiquitin ligases and associated factors that induce proteolytic cleavage and degradation of target proteins in response to TGF-b signaling [27,28,[50][51][52]. These interactions can cause proteolysis of HEF1/ NEDD9/Cas-L [28].…”

A New Central Scaffold for Metastasis: Parsing HEF1/Cas-L/NEDD9

“…Intriguingly, HEF1 binds directly to TGF-h pathway effectors and inhibitors, including multiple SMADs (e.g., ref. 18 and discussed in ref. 6).…”

Regulation of TGF-β signaling by Smad7

“…Jab1/CSN5, which is a component of the COP9 signalosome complex, also regulates the stability of Smad7 and releases Smad7-mediated suppression of TGF-b signaling [31]. Hic-5/ARA55 [32], Yes-associated protein (YAP65) [33], the salt-inducible kinase (SIK) [34], and Crk-associated substrate lymphocyte type (Cas-L) [35] are identified to be binding partners of Smad7 and regulate TGF-b signaling either positively or negatively. FKBP12, which is a cytoplasmic protein that binds to the immunosuppressant drugs, Tacrolimus (FK506) and rapamycin, has been found to interact with the GS region of type I receptors and inhibit signal transduction of TGF-b family [36].…”