EGF-Like domain of tenascin-C is proapoptotic for cultured smooth muscle cells.

OBJECTIVE: Based on our previous observations on the expression of Tenascin-C (Tn-C) in human atherosclerotic plaques and its colocalization with macrophages, we explored whether Tn-C undergoes fragmentation and the potential pathobiological significance of this fragmentation. METHODS AND RESULTS: Using cultured human smooth muscle cells (SMCs), we found that Tn-C upregulates expression of matrix metalloproteinases (MMPs). Western blot analysis revealed that Tn-C substrate is fragmented and most of the cleavage products have fibronectin-like and epidermal growth factor-like (EGF-like) domains of Tn-C. One fragment that contains an EGF-like domain was found in some human atherosclerotic plaques. Cell culture studies revealed that the recombinant EGF-like domain inhibits growth, induces apoptosis of SMCs in a dose-dependent, time-dependent, and caspase-dependent manner, and activates caspase-3 before SMC detachment. Conversely, the caspase inhibitor z-YVAD.cmk, serum, and protease inhibitors blocked cell apoptosis conferred by the EGF-like domain. In addition, these inhibitors blocked EGF-like domain-induced caspase-3 activation. In contrast to this EGF-like domain, intact Tn-C, its fibronectin-like, and its fibrinogen-like domains were inactive. CONCLUSIONS: Together with our previous observations, our data suggest that Tn-C upregulates MMP expression that cleaves Tn-C into fragments containing the EGF-like domain. This domain has proapoptotic activity for SMCs.

Balloon catheterization induces arterial expression of new Tenascin-C isoform.

Migration of smooth muscle cells (SMCs) across the internal elastic lamina is a key step in the development of atherosclerotic or restenotic plaques. Cell movement is a complex and highly dynamic phenomenon, involving the continuous formation and breakage of attachments with the underlying substratum. Tenascin-C (Tn-C), a counter-adhesive extracellular matrix protein, is comprised of several isoforms with distinct biological activities. Neither the structure nor function of these isoforms in SMCs has been defined. We have used primers and RT-PCR to fully identify Tn-C isoforms expressed by SMCs. Cloning and sequence analysis of the PCR product indicated that SMCs express a Tn-C isoform with only repeats A1 and A2 of fibronectin type III repeats. Using A1A2-specific antibodies, cDNA probes and RNase mapping, we observed that the A1A2 isoform is predominantly expressed by cultured SMCs derived from aorta of newborn rats, and its expression is up-regulated by PDGF-BB. In contrast, the expression of this isoform is markedly down-regulated in the SMCs derived from adult rat aorta. Western and Northern blots of injured rat carotid arteries revealed that the A1A2-isoform is expressed in response to injury. Using cultured SMCs, we found that the recombinant A1A2 protein that was found in the newly discovered Tn-C isoform promotes SMC chemotaxis. We conclude that Tn-C isoforms are expressed in a regulated fashion in vascular system. Our findings suggest a new role of Tn-C isoforms in the remodeling of vascular wall.