ASSOCIATION OF INFLUENZA-VIRUS NP AND M1 PROTEINS WITH CELLULAR CYTOSKELETAL ELEMENTS IN INFLUENZA VIRUS-INFECTED CELLS

We have investigated the association of the influenza virus matrix (M1 ) and nucleoprotein (NP) with the host cell cytoskeletal elements in i nfluenza virus infected MDCK and MDBK cells. At 6.5 h postinfection, t he newly synthesized M1 was Triton X 100 (TX-100) extractable but beca me resistant to TX-100 extraction during the chase with a t(1/2) of 20 min, NP, on the other hand, acquired TX-100 resistance immediately af ter synthesis. Significant fractions of both M1 and NP remained resist ant to differential detergent (Triton X-114, holamidopropyl)dimethylam monio]-1-propanesulfonate [CHAPS], octylglucoside) extraction, suggest ing that M1 and NP were interacting with the cytoskeletal elements. Ho wever, the high-molecular-weight form of the viral transmembrane prote in hemagglutinin (HA), which had undergone complex glycosylation, also became resistant to TX-100 extraction but was sensitive to octylgluco side detergent extraction, indicating that HA, unlike M1 or NP, was in teracting with TX-100-insoluble lipids and not with cytoskeletal eleme nts. Morphological analysis with cytoskeletal disrupting agents demons trated that M1 and NP were associated with microfilaments in virus-inf ected cells. However, M1, expressed alone in MDCK or HeLa cells from c loned cDNA or coexpressed with NP, did not become resistant to TX-100 extraction even after a long chase, NP, on the other hand, became TX-1 00 insoluble as in the virus-infected cells. M1 also did not acquire T X-100 insolubility in ts 56 (a temperature-sensitive mutant with a def ect in NP protein)-infected cells at the nonpermissive temperature. Fu rthermore, early in the infectious cycle in WSN-infected cells, M1 acq uired TX-100 resistance very slowly after a long chase and did not acq uire TX-100 resistance at all when chased in the presence of cyclohexi mide. On the other hand, late in the infectious cycle, M1 acquired TX- 100 resistance when chased in either the presence or absence of cycloh eximide. Taken together, these results demonstrate that M1 and NP inte ract with host microfilaments in virus-infected cells and that hll req uires other viral proteins or subviral components (possibly viral ribo nucleoprotein) for interaction with host cytoskeletal components. The implication of these results for viral morphogenesis is discussed.