Hexamethylene bisacetamide-induced differentiation of Friend virus-transformed murine erythroleukemia cells is associated with parallel changes in casein kinase II and guanine nucleotide exchange factor activities.
In mammalian cells, the guanine nucleotide exchange factor (GEF, eIF-2B) plays a major role in the regulation of initiation of protein synthesis. It catalyzes the exchange of eukaryotic chain initiation factor (eIF)-2-bound GDP for GTP and facilitates the recycling of eIF-2 during polypeptide chain initiation. We used the Friend virus-transformed murine erythroleukemia (MEL) cell system to elucidate the translational regulatory processes that occur during growth and hexamethylene bisacetamide (HMBA)-induced cell differentiation. GEF activity is increased during growth and decreased during MEL cell differentiation, and this parallels the overall changes in protein synthesis during this period. Inhibition of GEF activity in induced cells may occur indirectly by phosphorylation of the alpha-subunit of eIF-2. However, the decrease in GEF activity in induced cells cannot be reversed by increasing the concentration of eIF-2-GDP added as a substrate in the GEF assay. This is diagnostic for the presence of eIF-2 alpha(P)-GDP in cell lysates and suggests that regulation of GEF activity may occur by one or more mechanisms other than eIF-2(alpha) phosphorylation. We have previously shown that the activity of GEF may be influenced directly by phosphorylation with casein kinase II (CK-II) of the 82-kD subunit of the factor. CK-II activity parallels the changes in GEF activity and the rate of protein synthesis during growth and differentiation of MEL cells. Addition of 1mM spermidine, a stimulator of CK-II but not of purified GEF, in induced MEL cell extracts enhances both CK-II and GEF activities approximately 48 and 32%, respectively. The results presented suggest that the inhibition of protein synthesis during MEL cell differentiation may be linked to the decreased CK-II and GEF activities.
Aroor
A R
AR
Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216, USA.
Singh
L P
LP
Wahba
A J
AJ
D000081:Acetamides / Q000494:pharmacology*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D047390:Casein Kinase II; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002472:Cell Transformation, Viral / Q000187:drug effects; D002999:Clone Cells; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005622:Friend murine leukemia virus; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D004915:Leukemia, Erythroblastic, Acute; D008715:Methionine / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000096:biosynthesis; D014176:Protein Biosynthesis / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D013462:Sulfur Radioisotopes; D014407:Tumor Cells, Cultured
D000081:Acetamides; D000970:Antineoplastic Agents; D015852:Eukaryotic Initiation Factor-2; D009363:Neoplasm Proteins; D013462:Sulfur Radioisotopes; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D008715:Methionine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D019204:GTP-Binding Proteins; C014026:hexamethylene bisacetamide