Short RNA molecules with high binding affinity to the KH motif of A-kinase anchoring protein 1 (AKAP1): implications for the regulation of steroidogenesis.
One of the key regulators of acute steroid hormone biosynthesis in steroidogenic tissues is the steroidogenic acute regulatory (STAR) protein. Acute regulation of STAR production on the transcriptional level is mainly achieved through a cAMP-dependent mechanism, which is well understood. However, less is known about the posttranscriptional regulation of STAR synthesis, specifically the factors influencing the destiny of the Star mRNA after it leaves the nucleus. Here, we show that the 3'-untranslated region of Star mRNA interacts with the heterogeneous nuclear ribonucleoprotein K-homology (KH) motif of the mitochondrial scaffold A-kinase anchoring protein 1 (AKAP1) in vitro with a moderate affinity as measured by EMSAs. A mutation that mimics the phosphorylation state of the KH motif at a specific serine either did not alter, or had a negative impact on, protein-RNA binding under these conditions. The KH motif of AKAP1 binds short pyrimidine-rich RNA molecules with a stable hairpin structure as demonstrated by in vitro selection. AKAP1 also interacts with STAR mRNA in a dibutyryl-cAMP-stimulated human steroidogenic adrenocortical carcinoma cell line in vivo. Therefore, we propose a model in which AKAP1 anchors Star mRNA at the mitochondria, thus stabilizing the translational complex at this organelle, a situation that might affect STAR production and steroidogenesis. In addition, we suggest that the last 216 amino acid residues of AKAP1 might participate in the degradation of STAR and other nuclear-encoded mitochondrial mRNAs through interaction with a RNA-induced silencing complex, specifically with the argonaute 2 protein.
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
Petar N
PN
Grozdanov
Douglas M
DM
Stocco
D020413:3' Untranslated Regions / Q000235:genetics; D054758:A Kinase Anchor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D060565:Argonaute Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012739:Gonadal Steroid Hormones / Q000096:biosynthesis*; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D006801:Humans; D008928:Mitochondria / Q000235:genetics; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism; D016415:Sequence Alignment; D014158:Transcription, Genetic; D000098682:Steroidogenic Acute Regulatory Protein
D020413:3' Untranslated Regions; D054758:A Kinase Anchor Proteins; C105137:AKAP1 protein, human; D060565:Argonaute Proteins; D004268:DNA-Binding Proteins; D012739:Gonadal Steroid Hormones; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D010750:Phosphoproteins; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D000098682:Steroidogenic Acute Regulatory Protein; C072074:HNRNPK protein, human