The elevation of cellular phosphatidic acid levels caused by polyomavirus transformation can be disassociated from the activation of phospholipase D

Virology. 1997 Jul 7;233(2):392-401. doi: 10.1006/viro.1997.8630.

Abstract

Middle T (mT), the oncogene of murine polyomavirus, causes transformation of rat fibroblasts by activating a number of signal transducing pathways usually used by polypeptide growth factors and their receptors. Here, we report data regarding the activation of signal transducing pathways involving phospholipase D (PL-D). The hydrolysis of phospholipids by PL-D produces phosphatidic acid (PA), a compound with multiple biological effects. The PA content of cells expressing wild-type mT, introduced via a number of different methods, is approximately 50% higher than their untransformed counterparts. This increase in cellular PA content is associated with an approximately 65% increase in PL-D activity in cells expressing wild-type mT. We have also examined the effects of a number of site-directed mutants of mT, on both cellular PA levels and on PL-D activity. Mutants that do not produce mT (Py808A) or that produce a truncated, nonmembrane bound mT (Py1387T) have PA levels similar to that of control cells. Cells expressing the 322YF mutant of mT (which abolishes interaction of mT with phospholipase C gamma1) show increases in both PA levels and PL-D activity that are similar to those seen with wild-type mT. Expression of mutants that abolish the interaction of mT with either shc or with phosphatidylinositol 3-kinase (250YS and 315YF, respectively) cause an increase in PL-D activity comparable to that seen with wild-type mT. However, the PA content of cells expressing these mutants is not elevated. These results suggest that mT causes activation of cellular PL-D, but this activation alone is not sufficient to cause an increase in cellular PA content. Therefore, wild-type mT must affect another, as yet unknown, step in PA metabolism.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens, Polyomavirus Transforming / genetics
  • Antigens, Polyomavirus Transforming / metabolism*
  • Cell Line
  • Cell Transformation, Viral*
  • Diglycerides / metabolism
  • Fibroblasts / cytology
  • Fibroblasts / metabolism*
  • Fibroblasts / virology
  • Mice
  • Phosphatidic Acids / metabolism*
  • Phospholipase D / metabolism*
  • Polyomavirus / genetics
  • Polyomavirus / physiology*
  • Rats

Substances

  • Antigens, Polyomavirus Transforming
  • Diglycerides
  • Phosphatidic Acids
  • Phospholipase D