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.
Martinez
D A
DA
Department of Orthopaedics, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
Zuscik
M J
MJ
Ishibe
M
M
Rosier
R N
RN
Romano
P R
PR
Cushing
J E
JE
Puzas
J E
JE
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