5B). The number of fenestrae in Cas ΔSH3–expressing cells was 0.58 ± 0.16, which was statistically click here significantly low in comparison with those in parental and Cas FL–expressing NP31 cells (P < 0.001; left right bars and middle right bars in Fig. 5C). These results strongly indicate that Cas plays pivotal roles in the regulation of the actin cytoskeleton and in the formation of fenestrae in SECs. Cas is an adaptor/scaffold protein that contributes to various biological
processes through the regulation of actin stress fiber formation.9, 10 Upon physiological and pathological stimuli, Cas becomes tyrosine-phosphorylated mainly in the SD, which offers binding sites for the SH2 domain of downstream target molecules, including CrkII.9, 10 The Cas/CrkII complex sequentially activates downstream effectors, such as Rac and C3G, which consequently reorganize the actin cytoskeleton and finally define cellular dynamics.9, 10 We previously generated mice lacking Cas (Cas−/−) and demonstrated that they died in utero and exhibited cardiovascular anomalies.22 In the present study, we generated mice carrying a hypomorphic Cas allele lacking the exon 2–derived region. Exon 2 was targeted
in this study for several reasons. First, it is the only exon that encodes the whole region of a functional domain of Cas.8 Second, it encodes MK-8669 solubility dmso SH3, which binds to the proline-rich region of focal adhesion kinase11 and mediates the initial signaling event from the extracellular matrix to intracellular molecules.32, 33
Third, our previous compensation study revealed the importance of SD and SB for cell migration and cell transformation, respectively, but the role of SH3 is less understood.28 Mice harboring Cas with an exon 2 deletion (CasΔex2/Δex2) died as embryos (Table 1) but differed in phenotype from Cas−/− mice; CasΔex2/Δex2 mice exhibited impaired liver development with massive hepatocyte apoptosis (Fig. 2), and in contrast to Cas−/− mice, their cardiovascular system was preserved, presumably because of the conserved ability of Cas Δex2 to partially become tyrosine-phosphorylated and retain CrkII binding32 learn more (Fig. 4). In the former work,22 we noted that Cas−/− mice also showed retarded liver growth. We previously hypothesized it to be secondary to circulatory failure because the Cas protein was barely detectable in hepatocytes, as in this study22 (Fig. 3). However, the current observation that CasΔex2/Δex2 mice exhibit liver degeneration without suffering from cardiovascular anomalies strongly implies that dysfunction of Cas directly impairs liver development. The findings that Cas is preferentially expressed in SECs in the liver (Fig. 3) and that the expression patterns of Cas well correlate with the maturation of sinusoids (Supporting Fig. 1) indicate that Cas is functionally and developmentally involved in SECs and strongly suggest that Cas Δex2 impairs SEC function and leads to hepatocyte apoptosis.