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Bcl-2 and adenovirus E1B 19 kDA protein prevent E1A-induced processing of CPP32 and cleavage of poly(ADP-ribose)
1Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Abstract:
The E1A oncoproteins of adenovirus type 5 are potent inducers of apoptotic cell death. To manifest growth promoting and transforming properties, therefore, E1A requires the co-expression of a suppressor of apoptosis. During normal viral infection, this function is provided by the E1B 19 kDa protein. However, the cellular suppressor Bcl-2 can substitute for 19K during infection, and both proteins can effectively cooperate with E1A to facilitate transformation of primary cells in culture. How E1A induces apoptosis and at what point(s) on this pathway Bcl-2 and E1B 19K act are not presently known. Here, we demonstrate that E1A-induced apoptosis is accompanied by specific endo-proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), an event that is linked to the Ced-3/ICE apoptotic pathway in other systems. PARP cleavage was also observed in p53-null cells infected with 19K- virus expressing 13S E1A. In addition to PARP cleavage, expression of E1A caused processing of the zymogen form of CPP32, a Ced-3/ICE protease that cleaves PARP and is required for apoptosis in mammalian cells. These events were prevented when E1A was co-expressed with E1B 19K or BCL-2, which places these suppressors of apoptosis either at or upstream of processing of pro-CPP32.
Insights
Adenovirus E1A protein induces apoptosis by cleaving PARP and activating CPP32 protease. Apoptosis suppressors Bcl-2 and E1B 19K block these events, acting upstream of CPP32 activation.
Area of Science:
- Molecular Biology
- Cellular Biology
- Virology
Background:
- Adenovirus type 5 E1A oncoproteins induce apoptosis, requiring co-expression of apoptosis suppressors for transformation.
- The viral E1B 19 kDa protein and cellular Bcl-2 can substitute for each other in cooperating with E1A.
- The precise mechanism of E1A-induced apoptosis and the intervention points of Bcl-2 and E1B 19K remain unclear.
Purpose of the Study:
- To investigate the molecular pathway of E1A-induced apoptosis.
- To determine the role of poly(ADP-ribose) polymerase (PARP) cleavage and CPP32 protease activation in E1A-mediated cell death.
- To elucidate the mechanism by which Bcl-2 and E1B 19K suppress E1A-induced apoptosis.
Main Methods:
- Analysis of poly(ADP-ribose) polymerase (PARP) cleavage during adenovirus infection.
- Assessment of CPP32 protease processing in cells expressing E1A.
- Co-expression studies of E1A with apoptosis suppressors Bcl-2 and E1B 19K.
Main Results:
- E1A-induced apoptosis correlated with specific endo-proteolytic cleavage of PARP, a marker of the Ced-3/ICE apoptotic pathway.
- PARP cleavage was observed even in p53-null cells infected with E1A.
- E1A expression led to the processing of CPP32, a key protease for apoptosis, which was prevented by co-expression of E1B 19K or Bcl-2.
Conclusions:
- E1A induces apoptosis through the activation of the Ced-3/ICE pathway, involving PARP cleavage and CPP32 protease activation.
- E1B 19K and Bcl-2 function as apoptosis suppressors by acting at or upstream of CPP32 processing, thereby inhibiting E1A-induced cell death.