Mutation within the transmembrane domain of oxidized low-density lipoprotein receptor 1 influences oxidized low-density lipoprotein-induced signal transduction

ObjectiveTo investigate the important active sites within the NTFs to affect the <i>in vitro</i> interaction of oxidized low-density lipoprotein (ox-LDL) with its receptor, OLR1.MethodsSimulation analysis online was performed to generate various OLR1 chimeras, truncation mutants, and site-specific mutations. They were transfected in COS-7 cells and subjected to ox-LDL stimulations to observe the different reactions. Immunoprecipitation-mass spectrometry (IP-MS) was performed to show what proteins combined with OLR1 mutants in reaction to ox-LDL. Lipid uptake in human monocytes (THP-1) originated foam cells overexpressing somatic mutant of OLR1 were also determined. Further studies focusing on these regions were conducted using truncation mutants and site-specific mutants such as G43A, V44A, L45A, C46A, and L47A.ResultsAmino acids within the TM were highly conserved, spanning amino acids 35 to 57. The induction of intracellular p-ERK1/2 in response to ox-LDL stimulation was highly promoted in Chimera 3 possessing the TM from OLR1 like OLR1/WT (<i>p</i> < 0.05). Sequence alignment revealed two conserved regions within the TM of OLR1, Leu45-Cys46-Leu47 and Val55-Leu56-Gly57. Western blot showed that most of the TM changes ablated ERK1/2 activation in response to ox-LDL stimulation (<i>p</i> < 0.05). One human somatic mutation at L45F revealed significantly lower p-ERK1/2 levels with enhanced intake of ox-LDL in THP-1-derived foam cells than the control cells (<i>p</i> < 0.05). L45A and C46A molecular complexes were identified. After ox-LDL stimulation, these underlined interactions with keratins, namely KRT2 and KRT6A.ConclusionThese findings emphasize the vital role of the TM in the interactions between OLR1 and ox-LDL and point to an exciting possibility that signal transduction induced by ox-LDL through its receptor OLR1 may involve complex interactions with cytoskeletal proteins.