Intrinsic regulation of the interactions between the SH3 domain of p85 subunit of phosphatidylinositol-3 kinase and the protein network of BCR/ABL oncogenic tyrosine kinase.
OBJECTIVE
BCR/ABL fusion tyrosine kinase is responsible for the initiation and maintenance of the Philadelphia chromosome-positive chronic myelogenous leukemia (CML) and a cohort of acute lymphocytic leukemias. We show that a signaling protein, phosphatidylinositol-3 kinase (PI-3k), is essential for growth of CML cells, but not of normal hematopoietic cells, and that p85alpha subunit of PI-3k co-immunoprecipitates with BCR/ABL. Therefore, we made an attempt to better characterize p85alpha-BCR/ABL interactions.


METHODS
The mutants of p85alpha-SH3 domain were generated by in vitro site-directed mutagenesis system. Protein lysates were obtained from p210BCR/ABL-transformed murine 32Dcl3 myeloid cells, and in vitro transcription/translation was used to produce BCR/ABL protein. Pull-down and Western analyses were performed to detect the interaction between BCR/ABL and p85alpha-SH3. BCR/ABL-transformed 32Dcl3 cells were infected with internal ribosome entry site-green fluorescent protein retroviral construct encoding p85alpha-SH3 mutants to assess their biological effects.


RESULTS
We show here that the SH3 domain of p85alpha (p85alpha-SH3) pulls down the p210BCR/ABL kinase from hematopoietic cell lysates. The interaction between p85alpha-SH3 and BCR/ABL may be intermediated by proteins such as c-Cbl, Shc, Grb2, and/or Gab2. Mutations in the p85alpha-SH3 region responsible for proline-rich motif binding either abrogate or enhance these interactions. These mutants exert a modest inhibitory effect on growth factor-independent proliferation of BCR/ABL-positive 32Dcl3 cells.


CONCLUSIONS
Based on this information we speculate on the capability of p85alpha-SH3 to interact with the protein network of BCR/ABL oncoprotein.
Ren
Shu-yue
SY
Center for Biotechnology, College of Science and Technology, Temple University, 1900 N. 12th St, Philadelphia, PA 19122, USA.
Xue
Fan
F
Feng
Jan
J
Skorski
Tomasz
T
D019943:Amino Acid Substitution; D000818:Animals; D045744:Cell Line, Tumor; D016044:Fusion Proteins, bcr-abl; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010677:Philadelphia Chromosome; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D017354:Point Mutation / Q000235:genetics; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D018909:src Homology Domains / Q000235:genetics*
D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl