Identification of functional insulin-like growth factor-II/mannose-6-phosphate receptors in isolated bone cells.
The role of the IGF-II/cation independent mannose-6-phosphate (IGF-II/M6P) receptor in the transduction of cellular effects evoked by IGF-II has been extensively debated in the literature. Many reports suggest that IGF-II transduces its effects through the IGF-I receptor, while others show that IGF-II utilizes the type II receptor to affect cellular activity. This study 1) verifies the presence of the IGF-II/M6P receptor in rat calvarial osteoblasts, and 2) evaluates the ability of the receptor to initiate intracellular signals. Using conventional receptor binding assays, it was found that osteoblasts bind IGF-II with high affinity. Scatchard analyses indicated that there are 5.08 x 10(4) IGF-II/M6P receptors per osteoblast with a Kd near 2.0 nM). The receptor protein was further identified by cross-linking with 125I-IGF-II. Northern analysis was used to identify an mRNA transcript for the IGF-II/M6P receptor protein. To examine if the IGF-II/M6P receptor can initiate second messenger signals, the ability of IGF-II to evoke Ca2+ transients was evaluated. Osteoblasts pretreated with IGF-I did not lose their ability to respond to IGF-II. Further, a polyclonal antibody against the rat IGF-II/M6P receptor (R-II-PAB1) 1) was able to evoke its own Ca2+ response, and 2) was able to block the generation of Ca2+ transients caused by IGF-II. The data in this report show that the osteoblastic Ca2+ response to IGF-II appears to be caused by an intracellular release of Ca2+ which is mediated by the IGF-II/M6P receptor making it possible to envision how the receptor may be an important modulator of osteoblast mediated osteogenesis.
Department of Orthopaedics, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
D A
DA
Martinez
M J
MJ
Zuscik
M
M
Ishibe
R N
RN
Rosier
P R
PR
Romano
J E
JE
Cushing
J E
JE
Puzas
D000818:Animals; D015152:Blotting, Northern; D002118:Calcium / Q000502:physiology; D066298:In Vitro Techniques; D010006:Osteoblasts / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017527:Receptor, IGF Type 2 / Q000032:analysis* / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D013268:Stimulation, Chemical
D012333:RNA, Messenger; D017527:Receptor, IGF Type 2; D002118:Calcium