Deery W J, Gomer R H
Howard Hughes Medical Institute, Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA.
J Biol Chem. 1999 Nov 26;274(48):34476-82. doi: 10.1074/jbc.274.48.34476.
When Dictyostelium cells starve, they begin secreting a glycoprotein called conditioned medium factor (CMF). When there is a high density of starved cells, as indicated by a high concentration of CMF, the cells begin expressing some genes and aggregate using pulses of cAMP as a chemoattractant. CMF regulates gene expression via a G protein-independent pathway, whereas CMF regulates cAMP signal transduction via a G protein-dependent pathway. To elucidate receptors mediating cell density sensing, we used CMF-Sepharose to isolate membrane proteins that bind CMF. We identified a 50-kDa protein, CMFR1, that is sensitive to trypsin treatment of whole cells. We obtained partial amino acid sequence of CMFR1 and isolated the cDNA encoding it. The derived amino acid sequence has no significant similarity to known proteins and has two or three predicted transmembrane domains. Expression of CMFR1 in insect cells caused an increase in CMF binding. Repression of CMFR1 in Dictyostelium by gene disruption resulted in a approximately 50% decrease of the CMF binding and a loss of CMF-induced G protein-independent gene expression. The G protein-dependent CMF signal transduction pathways appear to be functional in cmfr1 cells, suggesting that cells sense the density-sensing factor CMF using two or more different receptors.
当盘基网柄菌细胞饥饿时，它们开始分泌一种名为条件培养基因子（CMF）的糖蛋白。当存在高密度的饥饿细胞时，如高浓度的CMF所示，细胞开始表达一些基因，并利用cAMP脉冲作为趋化剂进行聚集。CMF通过一条不依赖G蛋白的途径调节基因表达，而CMF通过一条依赖G蛋白的途径调节cAMP信号转导。为了阐明介导细胞密度感知的受体，我们使用CMF-琼脂糖来分离与CMF结合的膜蛋白。我们鉴定出一种50 kDa的蛋白CMFR1，它对胰蛋白酶处理全细胞敏感。我们获得了CMFR1的部分氨基酸序列，并分离出编码它的cDNA。推导的氨基酸序列与已知蛋白没有显著相似性，并且有两到三个预测的跨膜结构域。CMFR1在昆虫细胞中的表达导致CMF结合增加。通过基因破坏在盘基网柄菌中抑制CMFR1导致CMF结合减少约50%，并丧失CMF诱导的不依赖G蛋白的基因表达。依赖G蛋白的CMF信号转导途径在cmfr1细胞中似乎仍然起作用，这表明细胞使用两种或更多种不同的受体来感知密度感知因子CMF。
