We have investigated the role of the NPXY motif in the insulin-like growth factor I receptor (IGF-IR) by focusing on the activation of the phosphatidylinositol-3' kinase (PI3-K) pathway and DNA synthesis following IGF-I stimulation. For this purpose, we established stable R-cell lines, which are deficient in endogenous IGF-IR, and express human IGF-IR lacking the whole NPEY(950) sequence (DeltaNPEY). The DeltaNPEY cells showed an apparent autophosphorylation of IGF-IR, albeit with reduced sensitivity to stimulation compared with cells expressing similar levels of wild-type IGF-IR. Activation of insulin receptor substrate (IRS)-1 and IRS-2 was severely impaired in DeltaNPEY cells even at high concentrations of IGF-I. However, recruitment of p85, a regulatory subunit of PI3-K, to activated IRS-2 was similar between the cell lines, but recruitment of p85 to IRS-1 was reduced in DeltaNPEY cells. Essentially similar levels of p85- or phosphotyrosine-associated PI3-K and Akt activities were observed between the cell lines, although the sensitivity to stimulation was reduced in DeltaNPEY cells. Activation of extracellular signal-regulated kinase and DNA synthesis were virtually unaffected by the mutation, in terms of both sensitivity to stimulation and responsiveness. DNA synthesis was completely inhibited by the PI3-K inhibitor, LY294002. These results indicate that the IGF-IR is able to activate the PI3-K pathway and induce DNA synthesis in a normal fashion without the NPXY motif when the receptor is fully activated.
Search Results
You are looking at 1 - 3 of 3 items for
- Author: K Kataoka x
- Refine by Access: All content x
A. Nagasaka, S. Yoshida, A. Nakai, T. Ohyama, K. Iwase, S. Ohtani, H. Nakagawa, R. Masunaga, S. Kato, T. Kawabe, and K. Kataoka
ABSTRACT
Using hypophysectomized rats, it has been shown that DNA polymerase-β activity in the adrenal gland and testis is largely influenced by pituitary trophic hormones. Sucrose gradient centrifugation of thyroid extracts revealed three peaks of DNA polymerase-β activity sedimenting at 3·3S, 7·3S and 12S. Of these, hypophysectomy induced a decrease in the 3·3S DNA polymerase-β, whereas other molecular forms were affected only slightly. DNA polymerase-α and -γ activities were unaffected by hypophysectomy. These changes in DNA polymerase-β caused by hypophysectomy were reversed by daily i.p. injection of TSH. Furthermore, stimulation of the thyroid by excess TSH induced by the administration of 1-methyl-2-mercaptoimidazole resulted in an increase of all forms of thyroid DNA polymerase-β.
These results show that the level of DNA polymerase is relatively constant after hypophysectomy but that DNA polymerase-β in the rat thyroid gland is also modulated by TSH mainly through the change of activity of the polymerase-β which sediments at 3·3S.
J. Endocr. (1988) 119, 303–308
A. Nagasaka, H. Hidaka, H. Itoh, H. Nakagawa, K. Kataoka, A. Yamaguchi, K. Iwase, A. Nakai, T. Ohyama, T. Aono, S. Miyakawa, K. Kawase, and K. Miura
ABSTRACT
Adenylate cyclase and cyclic AMP phosphodiesterase activities in the thyroid gland were significantly reduced after hypophysectomy, followed by a gradual restoration of the enzyme activities to the levels seen in sham-operated rats whereas a slight and persistent reduction was evident in guanylate cyclase and cyclic GMP phosphodiesterase activities in the same tissue. These changes in enzyme activities were restored by TSH administration but not by ACTH. The recovery of activity produced by TSH administration was inhibited by cycloheximide. Hypophysectomy, or TSH and cycloheximide administration, did not produce any significant changes in the concentrations of calmodulin, suggesting that the alteration of these enzyme activities is not induced by a decrease in the concentration of calmodulin. Since forskolin activation of adenylate cyclase did not restore the reduced activity in the hypophysectomized rat thyroid to the level found in the sham-operated control rat thyroid, we conclude that there is a reduction of the amount of enzyme after hypophysectomy rather than a change of the active site on adenylate cyclase. The spontaneous restoration of adenylate cyclase and cyclic AMP phosphodiesterase activities after hypophysectomy implies that cyclic AMP-metabolizing enzymes are responsive to an autoregulatory mechanism in thyroid follicular cells.
J. Endocr. (1985) 105, 363–369
