EXPRESSION OF ENDOGENOUS NMDAR1 TRANSCRIPTS WITHOUT RECEPTOR PROTEIN SUGGESTS POST-TRANSCRIPTION CONTROL IN PC12-CELLS

Expression of RNA for the NMDAR1 subunit of the N-methyl-D-aspartate r eceptor was detected by Northern hybridization in both nerve growth fa ctor-differentiated and undifferentiated rat pheochromocytoma (PC12) c ells. The NMDA receptor type 1 (NMDAR1) message in PC12 cells was simi lar in size to that expressed in hippocampal neurons. PC12 cell cDNAs that were amplified by polymerase chain reaction with primers flanking the coding region of NMDAR1 corresponded to the NMDAR1 splice variant NMDA receptor type 1 isoform C (NMDAR1C). Using calcium imaging or pa tch-clamp recording, no functional NMDA-gated ion channels were found in PC12 cells. A monoclonal antibody against NMDAR1 was developed in o rder to investigate whether or not NMDAR1 protein was present in PC12 cells. Only trace amounts of NMDAR1 protein were found in native PC 12 cells. However, expression of NMDAR1 protein was detected in PC12 cel ls that were transfected with an expression vector containing an NMDAR 1C clone under control of a cytomegalovirus promoter. These findings s uggest that the expression of NMDAR1 protein in PC12 cells may be cont rolled by post-transcriptional mechanisms. The PC12 cell line may serv e as a model system for the study of the transcriptional, post-transcr iptional, and translational regulation of NMDAR1. Furthermore, the pre sence of NMDAR1 RNA in a particular cell type may not necessarily indi cate expression of NMDAR1 protein.