Primary lymphocytes can be stimulated to proliferate by mitogenic lectins such as concanavalin A (Con A). While the phorbol ester 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) alone is not mitogenic for these cells, it can enhance the response to Con A. Previously, protein kinases and phosphorylation have been reported to be important in lymphocyte proliferation. More recently TPA has been found to bind and activate protein kinase C. Therefore, we examined kinase activity in lymphocytes stimulated with the complete mitogen Con A and the comitogen TPA. In order to monitor more than one kinase we used an in situ gel assay and developed the system to compare both protein kinase C and cAMP‐dependent kinases. When total cell extracts were assayed in the presence of histone five major bands of activity were detected by autoradiography of the gel. The bands corresponding to protein kinase C and to cAMP‐dependent kinases were identified by partial purification of the enzymes, by binding of [20‐3H(N)]7‐phorbol‐12, 13‐dibutyrate (3H‐PDBU), and by photoaffinity labelling with 8‐azidoadenosine‐3′:5′‐cyclic monophosphate (8‐N3‐[32P]cAMP). Differential extraction of cell lysate allowed comparison of soluble and particulate kinases. We found that when the preparations from either TPA‐ or Con A‐treated lymphocytes were assayed, protein kinase C activity increased three‐ to four‐fold in the particulate fraction within 5 min after treatment. A concurrent decrease of 30–50% occurred in the cytosol. In contrast, cytosolic cAMP‐dependent protein kinase II increased 1.4‐fold in the same period with Con A. PKI and PKII showed the most significant changes after 24 h of stimulation by Con A when the activity of the holoenzyme decreased to half that of the unstimulated cells. Therefore, although TPA and Con A separately can affect protein kinase C this alone is not sufficient for proliferation to occur.
All Science Journal Classification (ASJC) codes
- Clinical Biochemistry
- Cell Biology