Measles virus matrix protein specifies apical virus release and glycoprotein sorting in epithelial cells

In polarized epithelial cells measles virus (MV) is predominantly released at the apical cell surface, irrespective of the sorting of its two envelope glycoproteins F and H, It has been reported previously that the viral matr ix (M) protein modulates the fusogenic capacity of the viral envelope glyco proteins. Here, extant MV mutants and chimeras were used to determine the r ole of M protein in the transport of viral glycoproteins and release of pro geny virions in polarized epithelial CaCo2 cells. In the absence of M, enve lope glycoproteins are sorted to the basolateral surface, suggesting that t hey possess intrinsic basolateral sorting signals. However, interactions of M with the glycoprotein cytoplasmic tails allow M-glycoprotein co-segregat ion to the apical surface, suggesting a vectorial function of M to retarget the glycoproteins for apical virion release. Whereas this may allow virus airway shedding, the intrinsic sorting of the glycoproteins to the basolate ral surface may account for systemic host infection by allowing efficient c ell-cell fusion.