Insulin-like growth factors (IGF) I and II utilize different calcium signaling pathways in a primary human parathyroid cell culture model.
BACKGROUND
In most cell types, influx of calcium (Ca2+) induces a growth or secretory response. The opposite occurs in parathyroid (PTH), cells where there is an inverse relationship between intracellular Ca2+ concentration and PTH secretion. We have examined the effects of calcium channel and metabolism modulators on insulin-like growth factors (IGFs) in a parathyroid cell culture model.


METHODS
Cell cultures were prepared from 9 patients undergoing operation for hyperparathyroidism. Following adhesion, the cells were transferred to serum-free medium and dosed with IGF I, II +/- ethyleneglycol-bis(beta-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), nifedipine, nickel, 2-aminoethoxy-diphenylborate (2-APB), or dantrolene. Proliferation (96 hours) was assessed by measuring tritiated thymidine incorporation and PTH release (1 and 3 hours) assayed by IRMA.


RESULTS
Both IGF I and II increased DNA synthesis to 162.8% +/- 10.6% (SEM) and 131.1% +/- 7.7%, respectively (P < 0.05). EGTA at 0.2 mmol (ionized Ca2+ 0.2 mmol) did not affect the response to both IGFs. EGTA at 2 mmol (ionized Ca2+ 0 mmol) reduced the DNA synthesis of IGF I and II to 29% and 26%, respectively (P < 0.05). Nifedipine and nickel (nonspecific Ca2+ channel blocker) were equally potent in negating the mitogenic effects of both IGFs. 2-APB (IP3R blocker) reduced the basal DNA synthesis to 51.3% +/- 8.4% but had no effect on either IGF. Dantrolene (ryanodine receptor blocker) negated IGF II induced mitogenisis (74.2% +/- 6.7%) and partially inhibited IGF I mitogenesis (123% +/- 6%) (P < 0.05). The rate of PTH secretion was greater after IGF II stimulation than after IGF I stimulation.


CONCLUSIONS
IGFs I and II induce mitogenesis by different calcium signaling pathways. These data suggest that parathyroid cells may utilize different calcium signaling pathways to distinguish growth factors and serum calcium changes.
Wong
C K M
CK
Department of Endocrine Surgery, Frenchay Hospital, Frenchay Park, Bristol, BS16 1LE, United Kingdom. christopher.wong@NBT.NHS.uk
Lai
T
T
Holly
J M P
JM
Wheeler
M H
MH
Stewart
C E H
CE
Farndon
J R
JR
D000704:Analysis of Variance; D020013:Calcium Signaling / Q000187:drug effects*; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D006961:Hyperparathyroidism / Q000378:metabolism / Q000601:surgery; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D008297:Male; D010280:Parathyroid Glands / Q000166:cytology* / Q000378:metabolism
D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II