BSF1 induces membrane protein phosphorylation but not phosphoinositide metabolism, Ca2+ mobilization, protein kinase C translocation, or membrane depolarization in resting murine B lymphocytes.
The findings presented in this study provide evidence that BSF1 receptors and mIg transmit signals via dissimilar transduction mechanisms that result in a common biologic response, hyper-Ia expression. Specifically, BSF1-containing supernatant does not induce PtdInsP2 hydrolysis as determined by measurement of PtdOH and InsP3. Additionally, BSF1 does not stimulate Ca2+ mobilization, PKC translocation from cytosol to membrane, or membrane depolarization. All of these metabolic events appear to play a central role in hyper-Ia expression mediated by mIg and are initiated after treatment of resting B cells with anti-Ig antibodies. In vitro phosphorylation studies with partially purified plasma membranes from resting B cells revealed that BSF1 interaction with membrane receptors stimulates a membrane-associated protein kinase that phosphorylates an endogenous protein of 44 KDa. Anti-Ig does not stimulate phosphorylation of the 44 KDa protein, suggesting that it does not activate the membrane-associated protein kinase. This observation provides the first evidence of a signal transduction mechanism associated with BSF1-receptor ligation. It indicates that although BSF1 does not modulate events associated with PKC activation, it may function via activation of a membrane-associated protein kinase. This provides a focal point for further studies directed at elucidating signal transduction resulting from BSF1-receptor interaction.
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000502:physiology; D006133:Growth Substances / Q000494:pharmacology*; D000949:Histocompatibility Antigens Class II / Q000032:analysis; D015847:Interleukin-4; D008222:Lymphokines / Q000494:pharmacology*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000502:physiology; D051379:Mice; D010716:Phosphatidylinositols / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D011971:Receptors, Immunologic / Q000502:physiology*
D000888:Antibodies, Anti-Idiotypic; D006133:Growth Substances; D000949:Histocompatibility Antigens Class II; D008222:Lymphokines; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D011971:Receptors, Immunologic; D015847:Interleukin-4; D011493:Protein Kinase C; D002118:Calcium