Differential effects of proinsulin C-peptide fragments on Na + , K + -ATPase activity of renal tubule segments

Abstract

Proinsulin C-peptide has been shown to stimulate the activity of Na+ K+ ATPase of rat renal tubule segments. Thirty-six peptides and amino acids, corresponding to parts of the intact rat C-peptide and suitable controls were screened for capacity to stimulate Na+, K+-ATPase in an attempt to determine potential active sites in the C-peptide molecule. The carboxy-terminal tetra and penta peptides were found to elicit 92-103% of the intact molecule's activity, and the remaining segment, des-(27-31) C-peptide, did not possess stimulatory activity. Peptides from the middle C-peptide segment, however, centering around a GGPEAG sequence, stimulated Na+, K+-ATPase activity (36-80% of the intact molecule's effect) but this effect was not balanced by corresponding inactivity of other parts. Furthermore, it was paralleled by activity of a non-native dipeptide D-form. It is concluded that the latter effect and that of the middle segment may represent complex interactions other than the apparently specific effects of the C-terminal segment.

C-Peptide stimulates Na+,K+-ATPase activity via PKC alpha in rat medullary thick ascending limb

“…C-peptide stimulation of Na + ,K + -ATPase activity in MTAL is in good agreement with previous studies that reported a concentration-dependent stimulation of Na + ,K + -ATPase activity by C-peptide in the rat proximal convoluted tubules (PCT) [6,7] and human erythrocytes [27,28]. However, in the PCT the threshold of C-peptide effect was about 1000 fold higher than in MTAL, and thus far above the physiological range.…”

“…Synthetic rat C-peptide II (amino acid sequence: EVEDPQVAQLELGGGPGAGDLQTLALEVARQ, from Ferring AB, Malmö, Sweden) was a kind gift of Dr. J. Wahren (Department of Clinical Physiology, Karolinska Institute, Stockholm, Sweden) and its purity was more than 99% as assessed by HPLC [7]. Rabbit polyclonal anti-Na + ,K + -ATPase α-subunit antibody raised against the rat holoenzyme was previously described [18].…”

“…Conversely, in experimental Type 1 diabetes, a situation with complete insulin and C-peptide deprivation, short term infusion of C-peptide increases renal functional reserve, reduces protein leakage and improves hyperfiltration [5]. At the cellular level, the effects of C-peptide include stimulation of Na + ,K + -ATPase activity [6,7] and activation of endothelial nitric oxide synthase [8,9,10]. The C-peptide signal transduction pathway is thought to involve an heteromultimeric G-protein-mediated increase in intracellular Ca 2+ leading to protein kinase C (PKC) and mitogen-activated protein kinase activation [4,6,11].…”

C-peptide stimulates ERK1/2 and JNK MAP kinases via activation of protein kinase C in human renal tubular cells

“…*p<0.05 vs control. A representative western blot image is shown in the upper panel of each graph Na + , K + -ATPase by this fragment [6,15,31,32], whereas scrambled C-peptide had no effect. In contrast to a previous study involving mouse endothelial cells [27], we did not observe an increase in p38 MAP kinase phosphorylation, which may be related to tissue-and speciesspecific differences.…”

“…Activation of MAP kinases is reported to result in cell proliferation [45], and an anti-apoptotic role of Akt/PKB stimulation has been demonstrated [46]. Subsequent activation of PKC and RhoA may also lead to Na + , K + -ATPase stimulation [6,47], a well-established effect of C-peptide in renal tubular cells [6,7,31]. Thus, signals transmitted by C-peptide are likely to play a crucial role in maintaining the number and function of proximal tubular cells.…”