Homodimerization of RBPMS2 through a new RRM-interaction motif is necessary to control smooth muscle plasticity.
Bottom Line: RBPMS2 contains only one RNA recognition motif (RRM) while this motif is often repeated in tandem or associated with other functional domains in RRM-containing proteins.We also show that this specific motif is conserved among its homologs and paralogs in vertebrates and in its insect and worm orthologs (CPO and MEC-8, respectively) suggesting a conserved molecular mechanism of action.Our study demonstrates that RBPMS2 possesses an RRM domain harboring both RNA-binding and protein-binding properties and that the newly identified RRM-homodimerization motif is crucial for the function of RBPMS2 at the cell and tissue levels.
Affiliation: INSERM U1046, Université Montpellier 1, Université Montpellier 2, 34295 Montpellier, France.Show MeSH
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Mentions: We then asked whether RBPMS2 homodimerization was required also for regulating SMC plasticity. To this aim, we established primary cultures of digestive differentiated SMCs in serum-free medium supplemented with insulin and BSA as previously published (9). After 3 days, in control SMC cultures, Calponin, an SMC contractile marker, was homogeneously expressed in highly organized filament bundles and cells were spindle-shaped (Figure 5A; Supplementary Figure S6). Conversely, in cells that express wild-type RBPMS2, Calponin expression was lost. Interestingly, SMCs expressing RBPMS2-L40E present no decrease of Calponin expression compared to control (Figure 5A). Moreover, after 6 days of culture, the number of cells that expressed phosphorylated histone 3-Ser10 (PH3), a standard marker of G2/M transition, was 4.5-fold higher in cultures that overexpress wild-type RBPMS2 than in control cells and SMC cells that express RBPMS2-L40E (Figure 5B), as also observed in heterologous DF1 cell line (Figure 4D). In addition, we also compared the impact of human RBPMS2, RBPMS2-L49E and L49Q in primary SMC culture and found that RBPMS2-L49Q like RBPMS2 induced an alteration of Calponin expression, whereas RBPMS2-L49E not (Supplementary Figure S3B). These results demonstrate that RBPMS2 homodimerization is essential to induce SMC dedifferentiation and proliferation.
Affiliation: INSERM U1046, Université Montpellier 1, Université Montpellier 2, 34295 Montpellier, France.