Novel serine phosphorylation of pp60c-src in intact cells after tumor promoter treatment

High-throughput protease activity cytometry reveals dose-dependent heterogeneity in PMA-mediated ADAM17 activation

As key components of autocrine signaling, pericellular proteases, a disintegrin and metalloproteinases (ADAMs) in particular, are known to impact the microenvironment of individual cells and have significant implications in various pathological situations including cancer, inflammatory and vascular diseases. There is great incentive to develop a high-throughput platform for single-cell measurement of pericellular protease activity, as it is essential for studying the heterogeneity of protease response and the corresponding cell behavioral consequences. In this work, we developed a microfluidic platform to simultaneously monitor protease activity of many single cells in a time-dependent manner. This platform isolates individual microwells rapidly on demand and thus allows single-cell activity measurement of both cell-surface and secreted proteases by confining individual cells with diffusive FRET-based substrates. With this platform, we observed dose-dependent heterogeneous protease activation of HepG2 cells treated with phorbol 12-myristate 13-acetate (PMA). To study the temporal behavior of PMA-induced protease response, we monitored the pericellular protease activity of the same single cells during three different time periods and revealed the diversity in the dynamic patterns of single-cell protease activity profile upon PMA stimulation. The unique temporal information of single-cell protease response can help unveil the complicated functional role of pericellular proteases.

src-related protein tyrosine kinases and their surface receptors

The CD4-p56lck and CD8-p56lck complexes have served as a paradym for an expanding number of interactions between src-family members (p56lck, p59fyn, p56lyn, p55blk) and surface receptors. These interactions implicate src-related kinases in the regulation of a variety of intracellular events, from lymphokine production and cytotoxicity to the expression of specific nuclear binding proteins. Different molecular mechanisms appear to have evolved to facilitate the receptor-kinase interactions, including the use of N-terminal regions, SH2 regions and kinase domains. Variation exists in stoichiometry, affinity and the nature of signals generated by these complexes in cells. The CD4-p56lck complex differs from receptor-tyrosine kinases in a number of important ways, including mechanisms of kinase domain regulation and recruitment of substrates such as PI 3-kinase. Furthermore, they may have a special affinity for receptor-substrates such as the TcR zeta, MB1/B29 or CD5 receptors, and act to recruit other SH2-carrying proteins, such as ZAP-70 to the receptor complexes. Receptor-src kinase interactions represent the first step in a cascade of intracellular events within the protein-tyrosine kinase/phosphatase cascade.

Matrix mineralization in hypertrophic chondrocyte cultures. Beta glycerophosphate increases type X collagen messenger RNA and the specific activity of pp60c-src kinase

The phenomenon of chondrocyte hypertrophy is accompanied by the expression of type X collagen and the appearance of matrix mineralization. These events are also associated with changes in the phosphorylation of intracellular proteins. In this study the addition of 10 mM beta-glycerophosphate to hypertrophic chondrocytes resulted in stimulation of type X collagen synthesis up to 10 days in culture and an increase in the expression of type X collagen mRNA. This was followed by the onset of mineralization and the appearance of calcium hydroxyapatite. In contrast, the addition of beta-glycerophosphate to non-hypertrophic chondrocytes failed to induce expression of type X collagen or to produce changes in calcium and phosphate. The increased formation of type X collagen and of mineral in hypertrophic chondrocytes was accompanied by changes in the tyrosine kinase pp60c-src. While the level of c-src protein decreased approximately 2.5-fold in hypertrophic chondrocytes after 17 days of beta-glycerophosphate treatment, the specific activity of pp60c-src kinase increased approximately 3-fold in the cells that could be induced to mineralize but remained unchanged in cells that did not exhibit this property. Regulation of kinase activity may be an important event in endochondral ossification.

Role of tyrosine kinases in bombesin regulation of gastric mucosal proliferative activity in young and aged rats

In vivo and in vitro experiments were performed to examine the responsiveness of the gastric mucosa to the growth-promoting action of bombesin in young (4 months) and aged (22 months) Fischer 344 rats. In addition, the role of tyrosine kinase (Tyr-K) in regulating this action of bombesin was also examined. In young rats, infusion of bombesin (300 ng/kg/h) by osmotic minipump for 2 weeks resulted in a significant 100% increase in mucosal DNA synthesis and ornithine decarboxylase (ODC) activity. These increases were accompanied by a 32% (p less than 0.025) rise in gastric mucosal overall Tyr-K activity and a 71% (p less than 0.001) increase in Tyr-k activity associated with pp60c-src, when compared with the corresponding controls. The bombesin-induced stimulation of pp60c-src Tyr-k activity was also associated with a 25% increase in phosphorylation of this protein. In contrast, in aged rats, none of these parameters were affected by bombesin. A similar phenomenon was also observed when mucosal explants from young and aged rats were exposed to bombesin in an organ culture system. Exposure of gastric mucosal explants from young, but not from aged, rats to 10(-8) M bombesin for 8 h resulted in a 300% (p less than 0.001) increase in ODC activity, a 150% (p less than 0.001) rise in Tyr-k activity, and a marked increase (400-600%) in tyrosine-specific phosphorylation of three membrane proteins with M(r) of 55, 44, and 41 kDa, when compared with the corresponding controls. However, these increases were totally abolished by genistein, a specific irreversible inhibitor of Tyr-k.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinase activity and genetic characterization of a growth related antigen of Drosophila

The Drosophila developmental antigen recognized by the monoclonal antibody F7D6 is expressed in dividing embryonic and imaginal cells but is lost from all differentiating tissues except electrogenic cells of the nervous system and spontaneously contracting muscles. The 63 kDa antigen is associated with the inner surface of plasma membranes and is expressed in several classes of tumorous mutants of Drosophila. The monoclonal antibody was used for immunoprecipitating the antigen for biochemical characterization and for screening expression vector cDNA libraries. Here we report that this oncodevelopmental antigen is a phosphoprotein and a serine-threonine specific protein kinase. A 1.6 kb cDNA isolated by immunological screening of an ovarian library hybridized to a single band on polytene chromosomes, localizing the gene to 72F on the left arm of the third chromosome. Immunofluorescence assays of deficiency stocks in the region confirmed the location of the gene and identity of the cDNA clone, and mapped the gene between the left breakpoints of Df(3L) st100.62 and Df(3L) stj7, i.e., between 72F3-7 and 73A1-2. The biochemical and genetic properties indicate that this is a novel growth-related kinase of Drosophila.

Purified maturation promoting factor phosphorylates pp60c-src at the sites phosphorylated during fibroblast mitosis

We have previously shown that overexpressed chicken pp60c-src has retarded mobility, novel serine/threonine phosphorylation, and enhanced kinase activity during NIH 3T3 cell mitosis. Here we show that novel mitotic phosphorylations occur at Thr 34, Thr 46, and Ser 72. The possibility, previously raised, that Ser 17 is dephosphorylated during mitosis is excluded. The phosphorylated sites lie in consensus sequences for phosphorylation by p34cdc2, the catalytic component of maturation promoting factor (MPF). Furthermore, highly purified MPF from metaphase-arrested Xenopus eggs phosphorylated both wild-type and kinase-defective pp60c-src at these sites. Altered phosphorylation alone is sufficient to account for the large retardation in mitotic pp60c-src electrophoretic mobility: phosphorylation of normal pp60c-src by MPF retarded mobility and dephosphorylation of mitotic pp60c-src restored normal mobility. These results suggest that pp60c-src is one of the targets for MPF action, which may account in part for the pleiotropic changes in protein phosphorylation and cellular architecture that occur during mitosis.

Structural requirements of diacylglycerols for binding and activating phospholipid-dependent, Ca++-sensitive protein kinase

Phospholipid-dependent, Ca++-sensitive protein kinase (protein kinase C) is activated by phorbol esters and diacylglycerols. A series of diacylglycerols was synthesized with different substituents at positions 1 and 2 in order to expand known structure-activity relationships for these compounds with respect to binding and activating purified protein kinase C. Compounds were synthesized with saturated and unsaturated long chain fatty acyl groups at position 1 and acetyl, butyryl, or hexanoyl groups at position 2. Binding to protein kinase C correlated well with in-vitro activation of the enzyme. These diacylglycerols activated protein kinase C in an intact cellular system causing the phosphorylation of pp60c-src. This indicates that the length of the fatty acyl group at C2 is critical and that the existence of unsaturation in the fatty acyl group at C1 is not essential.

Phosphorylation of pp60v-src by the TPA receptor kinase (protein kinase C)

Incubation of pp60v-src with the purified 12-O-tetradecanoyl-13-acetate (TPA) receptor kinase (protein kinase C) resulted in an increase in the phosphorylation of pp60v-src. Two-dimensional tryptic phosphopeptide mapping showed that three major phosphoserine containing peptides were labeled which were localized within the amino terminal 18,000 Da of the src protein. Based on comparative tryptic mapping, one of these major phosphopeptides was identical to the peptide labeled on pp60v-src immunoprecipitated from cells labeled with [32P]orthophosphate and treated with TPA. These data suggest that a direct interaction takes place between protein kinase C and pp60v-src.