Stimulation of the exocrine pancreas by cholecystokinin (CCK) is associated with alterations in cellular Ca++ and protein phosphorylation. In other tissue systems, Ca++ directed metabolism often appears to be regulated by the Ca++ binding protein Calmodulin (CDR).
The aim of this investigative effort is to elucidate an interaction between Ca++, CDR and protein phosphorylation in the exocrine pancreas. Recent work from this laboratory demonstrated that in situ, stimulation of the pancreas by CCK results in the phosphorylation of the ribosomal protein S6. In a cell-free system, an identical pattern of S6 phosphorylation can be obtained using purified ribosomes as the substrate and pancreatic postmicrosomal supernatant (PS4) the protein kinase (PK) donor. This PK activity is dependent on both Ca++ and CDR and can be enriched for and separated from a cyclic AMP or Ca++/phospholipid regulated PK present in PS4 by their substrate specificity and salt elution from a DEAE cellulose column. Using 125I-CDR overlay of proteins separated by SDS-PAGE to identify CDR binding proteins (CDR-Bp), a 5.6Kd CDR-Bp co-elutes with the Ca++/CDR-PK from the DEAE column. In addition, the major CDR-Bp in pancreas is also a 55 Kd protein. Efforts are underway to purify this Ca++/DCR-PK by gel filtration and affinity chromatography. Preliminary evidence suggests that this type of Ca++/CDR-PK may be common to tissues that respond to neurohumoral stimulation with exocytosis. The importance of ribosomal S6 phosphorylation may be that it serves as an important pivotal point in the control of m-RNA translation. To address these two hypotheses in the exocrine pancreas will require further characterization and purification of the Ca++/CDR-PK as outlined in this proposal.
| Marino, C R; Castle, J D; Gorelick, F S (1990) Regulated phosphorylation of secretory granule membrane proteins of the rat parotid gland. Am J Physiol 259:G70-7 |
