The heterogeneity of protein kinase C in various rat tissues

Expression of multiple subspecies of protein kinase C (PKC) was studied in various rat tissues. Three types of the enzyme designated type I, II, and III were analyzed, which have the structures of gamma-, beta- (beta I- and beta II-), and alpha-sequence, respectively. Type I enzyme was found only in the central nervous tissue, whereas type III enzyme appeared to be commonly present in various tissues such as liver, spleen, lung, testis, heart, and kidney. Type II enzyme was also found in these tissues. However, immunoblot and biochemical analysis indicated that type II enzyme of lung and heart was distinct from that of other tissues. The tissue-specific expression of PKC suggests that each subspecies of this enzyme has a defined function in processing and modulating tissue responses to external stimuli.     

Inhibition of [3H]MK-801 Binding by Ferrous (II) but Not Ferric (III) Ions in a Manner Different from That by Sodium Nitroprusside (II) in Rat Brain Synaptic Membranes

Abstract: The addition of sodium nitroprusside (SNP) significantly inhibited binding of (+)-5-[³H]methyl-10,11-dihydro-5 H -dibenzo[ a,d ]cyclohepten-5,10-imine ([³H]MK-801) to an ion channel associated with the N -methyl- d -aspartate (NMDA) receptor in a concentration-dependent manner at concentrations of >1 µ M in rat brain synaptic membranes not extensively washed. However, neither S -nitroso- N -acetylpenicillamine nor S -nitroso- l -glutathione inhibited binding even at 100 µ M . Of the two compounds structurally related to SNP (II), similarly potent inhibition was induced by potassium ferrocyanide (II) but not by potassium ferricyanide (III). In addition, ferrous chloride (II) induced much more potent inhibition of binding than ferric chloride (III), at a similar concentration range. In contrast, iron chelators prevented the inhibition by ferrous chloride (II) without markedly affecting that by SNP (II) and potassium ferrocyanide (II). Pretreatment with ferrous chloride (II) also led to potent inhibition of [³H]MK-801 binding in a manner insensitive to subsequent addition of the iron chelators. Pretreatment with Triton X-100 resulted in significant potentiation of the ability of ferrous chloride (II) to inhibit [³H]MK-801 binding irrespective of the addition of agonists, moreover, although binding of other radioligands to the non-NMDA receptors was unaltered after pretreatment first with Triton X-100 and then with ferrous chloride (II). These results suggest that ferrous ions (II) may interfere selectively with opening processes of the NMDA channel through mechanisms entirely different from those underlying the inhibition by both SNP (II) and potassium ferrocyanide (II) in rat brain.     

Multiple forms of cytochrome P-450 from kidney cortex microsomes of rabbits treated with phenobarbital

Two distinct forms of cytochrome P-450 (P-450), referred to as P-450a and P-450b, were separated and purified from kidney cortex microsomes of rabbits treated with phenobarbital. P-450a had a monomeric molecular weight of 53,000, and its CO-reduced difference spectral peak was at 450 nm. It catalyzed the omega-hydroxylation of prostaglandin A1 (PGA1), and the omega- and (omega-1)-hydroxylation of myristate, but it was inactive toward exogenous compounds tested. On the other hand, P-450b had a monomeric molecular weight of 49,000, and its CO-reduced difference spectral peak was at 451 nm. This cytochrome was not able to hydroxylate PGA1 at all. It hydroxylated myristate much more slowly than P-450a, and preferentially at the (omega-1)-position. Unlike P-450a, P-450b efficiently metabolized exogenous compounds such as benzphetamine, aminopyrine, 7-ethoxycoumarin and p-nitroanisole. It is suggested that P-450a and P-450b are specialized for the metabolism of PGA1 and exogenous compounds, respectively, in kidney cortex microsomes.     

Electrophoretic analysis of pancreatic proteases and zymogen-activating factors in the mouse

Mouse pancreatic proteases were analyzed by one- and two-dimensional electrophoresis. Active proteases that existed in the luminal fluid were separated into at least eight bands in 8% polyacrylamide gel. Pancreatic proteases activated by intestinal extract were separated into at least seven bands. The mobilities of these bands were exactly the same as those of proteases in the luminal fluid except for those of the most cathodal band. Two kinds of trypsin (Try-I group and Try-II) and one kind of chymotrypsin (Chy-I) were determined by specific and nonspecific protease staining. Try-I group and Try-II were derived from different trypsinogens (Try G-I group and Try G-II), whereas Chy-I was derived from a single chymotrypsinogen (Chy G). Although Try G-II was activated by both intestinal extract and by bovine trypsin, Try G-I group activated only by intestinal extract. Intestinal-activating factors were analyzed by two-dimensional electrophoresis. Mouse enterokinase (enteropeptidase EC 3.4.4.8), which can activate bovine trypsinogen, had a slow mobility. In the intestine of the mouse there are several activating factors in addition to enterokinase. Although it is unclear what intestinal-activating factors can activate Chy G, there is a factor that can convert chymotrypsinogen into chymotrypsin directly. These data suggest that intestinal-activating factors play an important role in the activating mechanisms of mouse pancreatic zymogens.     

Characterization of protein kinase C from normal and transformed cultured murine fibroblasts

Protein kinase C of normal and ras-transformed NIH 3T3 cells was purified by chromatography on TSK DEAE-5PW, threonine-Sepharose, and TSK phenyl-5PW columns. Comparison of the fibroblast enzyme with several types of rat brain protein kinase C by chromatography on a hydroxyapatite column and by immunoblotting, indicates that both normal and transformed fibroblasts possess only one of the four subspecies of protein kinase C which have been identified in brain tissues. This subspecies presumably has the structure encoded by alpha-sequence or a closely related sequence. No significant difference was seen between those enzymes purified from normal and transformed fibroblasts.     

Adaptor protein Crk is required for ephrin-B1-induced membrane ruffling and focal complex assembly of human aortic endothelial cells

Endothelial cell migration is an essential step in vasculogenesis and angiogenesis, in which receptor tyrosine kinases play a pivotal role. We investigated the mechanism by which ephrin-B1 promotes membrane ruffling in human aortic endothelial cells, because membrane ruffling heralds cell body migration. We especially focused on the role of Crk adaptor protein in EphB-mediated signaling. Using DsRed-tagged Crk and a fluorescent time-lapse microscope, we showed that Crk was recruited to the nascent focal complex after ephrin-B1 stimulation. Furthermore, we found that p130(Cas), but not paxillin, recruited Crk to the nascent focal complex. The necessity of Crk in ephrin-B1-induced membrane ruffling was shown both by the overexpression of dominant negative Crk mutants and by the depletion of Crk by using RNA interference. Then, we examined the role of two major downstream molecules of Crk, Rac1 and Rap1. The dominant negative mutant of Rac1 completely inhibited ephrin-B1-induced membrane ruffling and focal complex assembly. In contrast, rap1GAPII, a negative regulator of Rap1, did not inhibit ephrin-B1-induced membrane ruffling. However, in rap1GAPII-expressing cells, ephrin-B1 did not induce membrane spreading, probably due to instability of the focal complex. These results indicated that Crk plays a critical role in Rac1-induced membrane ruffling and Rap1-mediated nascent focal complex stabilization contributing to ephrin-B1-induced human aortic endothelial cells migration.     

Catalytic properties of yeast protein kinase C: difference between the yeast and mammalian enzymes.

With bovine myelin basic protein as a model common substrate, protein kinases C (PKC) purified from yeast (Saccharomyces cerevisiae) and mammalian tissue (rat brain) were shown to exhibit clearly different catalytic properties. The major sites of phosphorylation in bovine myelin basic protein by the yeast PKC were identified: Thr-19, Thr-34, and Thr-65. These sites are distinctly different from those for the mammalian PKC: Ser-8, Ser-46, Ser-55, Ser-110, Ser-132, Ser-151, and Ser-161, which were previously identified [Kishimoto, A., Nishiyama, K., Nakanishi, H., Uratsuji, Y., Nomura, H., Takeyama, Y., & Nishizuka, Y. (1985) J. Biol. Chem. 160, 12492-12499]. The results suggest that the yeast and mammalian enzymes may play distinct roles in cellular regulation. No evidence is available, however, that a yeast-type PKC exists in mammalian tissues. An oligopeptide containing the sequence around Thr-19 of bovine myelin basic protein, Lys-Tyr-Leu-Ala-Ser-Ala-Ser-Thr(19)-Met-Asp-His-Ala, can be used as a substrate for selective assaying of the yeast PKC.