Atwood et al. BMC Genomics 2011, 12:14 http://www.biomedcentral.com/1471-2164/12/14 Page 9 of 14 Figure 6 mRNA expression analysis of GPCR related signaling proteins. Microarray analysis of mRNA levels of GPCR related signaling proteins for HEK293, AtT20, BV2 and N18 cell lines. The gray lines indicate the threshold of statistical significance and the dark bars are proteins for which statistically significant levels of mRNA were detected. White bars indicate levels of mRNA for proteins that were present, but did not reach statistical significance. Abbreviations: ND = Not determined; PLA = Phospolipase A; PLC = Phospholipase C; PLD = Phospholipase D; RGS = Regulator of G protein signaling. data examining the presence of several hundred differ- ent GPCRs and related signaling proteins in four phe- notypically diverse cell lines frequently used in GPCR research. HEK293 cells are perhaps the most widely used cell line, cited in over four thousand publications and initial work has identified a number of endogenous receptors (see below). We expanded upon this knowledge by demonstrating that HEK293 cells express at least 75 dif- ferent GPCR mRNAs. Much of what has been reported about GPCR mRNA expression patterns in HEK293 cells was confirmed by our analysis: ADORA2B, CHRM3, F2R, F2RL1, GABABR1, GPCR5A, GPR19, LGR5, LPAR1, LPAR2, P2YR1, PTGER2, S1PR, and SSTR5 [17,26,38-46]. HEK293 cells have been reported to possess mRNA for a number of receptors that were not found to be expressed at statistically significant levels in our study: 5HT1D, 5HT6, 5HT7, ADRA2(a-c), ADRAB2, AGTR1, BDKRB2, DRD2, GPR1, GPR161, GRM4, P2YR2 and SSTR2 [17,26,46-50]. Our results also indicate that HEK293 cells express mRNA for most G protein subunit isoforms, and numerous isoforms of adenylyl cyclase, protein kinases A and C, and phospho- lipase C. In addition they are useful for studying