TY - JOUR
T1 - Plasma distribution and signaling activities of IGF-II precursors
AU - Marks, Alicia G.
AU - Carroll, Julie M.
AU - Purnell, Jonathan Q.
AU - Roberts, Charles T.
PY - 2011/3
Y1 - 2011/3
N2 - IGF-II is thought to function through activation of the IGF-I receptor (IGF-IR) and the A isoform of the IR, with the IGF-IR being relevant to tumorigenesis and the IR to both tumorigenesis and metabolic control. In the paraneoplastic syndrome of nonislet cell tumor hypoglycemia, tumor-derived IGF-II has been proposed to exert both proliferative and metabolic effects, exemplifying this dual mode of action. Increased levels of IGF-II precursors ("big" and pro-IGF-II) have been reported in the circulation of nonislet cell tumor patients and have been proposed to exert greater or different effects than mature IGF-II. However, most studies have not defined which version is being investigated, and the relative activation of the IR and IGF-IR by IGF-II precursors has not been delineated. In this study,wedetermined the distribution of IGF-II isoforms in normalhumanplasma and their ability to activate the alternative versions of the IR. The majority (71%) of total IGF-II in human plasma was the mature form, while "big" and pro-IGF-II comprised 16% and 13%, respectively, with more variation seen in the levels of mature IGF-II. In IGF-IR- deficient cells expressing similar levels of human IR-A or IR-B, mature and "big" IGF-II exhibited similar activation of IR signaling, while pro-IGF-II exhibited significantly less activation. Downstream activation of Akt by mature and "big" IGF-II was greater in IR-A cells, consistent with previous reports of the greater affinity of IR-A for IGF-II. Thus, both IGF-II precursor forms are present in human plasma but do not preferentially activate the IR.
AB - IGF-II is thought to function through activation of the IGF-I receptor (IGF-IR) and the A isoform of the IR, with the IGF-IR being relevant to tumorigenesis and the IR to both tumorigenesis and metabolic control. In the paraneoplastic syndrome of nonislet cell tumor hypoglycemia, tumor-derived IGF-II has been proposed to exert both proliferative and metabolic effects, exemplifying this dual mode of action. Increased levels of IGF-II precursors ("big" and pro-IGF-II) have been reported in the circulation of nonislet cell tumor patients and have been proposed to exert greater or different effects than mature IGF-II. However, most studies have not defined which version is being investigated, and the relative activation of the IR and IGF-IR by IGF-II precursors has not been delineated. In this study,wedetermined the distribution of IGF-II isoforms in normalhumanplasma and their ability to activate the alternative versions of the IR. The majority (71%) of total IGF-II in human plasma was the mature form, while "big" and pro-IGF-II comprised 16% and 13%, respectively, with more variation seen in the levels of mature IGF-II. In IGF-IR- deficient cells expressing similar levels of human IR-A or IR-B, mature and "big" IGF-II exhibited similar activation of IR signaling, while pro-IGF-II exhibited significantly less activation. Downstream activation of Akt by mature and "big" IGF-II was greater in IR-A cells, consistent with previous reports of the greater affinity of IR-A for IGF-II. Thus, both IGF-II precursor forms are present in human plasma but do not preferentially activate the IR.
UR - http://www.scopus.com/inward/record.url?scp=79951861980&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79951861980&partnerID=8YFLogxK
U2 - 10.1210/en.2010-0784
DO - 10.1210/en.2010-0784
M3 - Article
C2 - 21285309
AN - SCOPUS:79951861980
SN - 0013-7227
VL - 152
SP - 922
EP - 930
JO - Endocrinology
JF - Endocrinology
IS - 3
ER -