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cDNA cloning, expression studies and chromosome mapping of human type I serine/threonine kinase receptor ALK7
J Bondestam1, M A Huotari, A Morén
1Program for Developmental and Reproductive Biology, Biomedicum Helsinki, Helsinki, Finland. jonas.bondestam@helsinki.fi
Abstract:
Transforming growth factor-beta (TGF-beta) superfamily related growth factors signal by binding to transmembrane type I and type II receptor serine/threonine kinases (RSTK), which phosphorylate intracellular Smad transcription factors in response to ligand binding. Here we describe the cloning of the human type I RSTK activin receptor-like kinase 7 (ALK7), an orthologue of the previously identified rat ALK7. Nodal, a TGF-beta member expressed during embryonic development and implicated in developmental events like mesoderm formation and left-right axis specification, was recently shown to signal through ALK7. We found ALK7 mRNA to be most abundantly expressed in human brain, pancreas and colon. A cDNA encoding the open reading frame of ALK7 was obtained from a human brain cDNA library. Furthermore, a P1 artificial chromosome (PAC) clone containing the human ALK7 gene was isolated and fluorescent in situ hybridization (FISH) on metaphase chromosomes identified the gene locus as chromosome 2q24.1-->q3. To test the functionality of the ALK7 signaling, we generated recombinant adenoviruses containing a constitutively active form of ALK7 (Ad-caALK7), which is capable of activating downstream targets in a ligand independent manner. Infection with Ad-caALK7 of MIN6 insulinoma cells, in which ALK7 has previously been shown to be endogenously expressed, led to a marked increase in the phosphorylation of Smad2, a signaling molecule also used by TGF-betas and activins.
Insights
Researchers cloned the human activin receptor-like kinase 7 (ALK7) gene, crucial for transforming growth factor-beta superfamily signaling. ALK7 activation phosphorylates Smad2, indicating its role in cellular pathways.
Area of Science:
- Molecular Biology
- Cell Signaling
- Genetics
Background:
- Transforming growth factor-beta (TGF-beta) superfamily members utilize receptor serine/threonine kinases (RSTKs) to signal.
- Intracellular Smad transcription factors are phosphorylated upon ligand binding to these receptors.
- Activin receptor-like kinase 7 (ALK7) is a type I RSTK implicated in developmental signaling pathways.
Purpose of the Study:
- To clone the human activin receptor-like kinase 7 (ALK7) gene.
- To determine the gene locus of human ALK7.
- To functionally test ALK7 signaling in human cells.
Main Methods:
- Cloning of human ALK7 cDNA from a brain library.
- Isolation of a PAC clone containing the ALK7 gene.
- Fluorescent in situ hybridization (FISH) for gene locus identification.
- Generation of recombinant adenoviruses with constitutively active ALK7 (Ad-caALK7).
- Infection of MIN6 insulinoma cells with Ad-caALK7.
Main Results:
- Human ALK7 was cloned and its gene locus identified as chromosome 2q24.1-->q3.
- ALK7 mRNA expression was highest in human brain, pancreas, and colon.
- Constitutively active ALK7 (Ad-caALK7) significantly increased Smad2 phosphorylation in MIN6 cells.
- Nodal, a TGF-beta member, signals through ALK7.
Conclusions:
- The human ALK7 gene has been successfully cloned and characterized.
- Functional studies confirm ALK7's role in Smad2 phosphorylation, a key signaling event.
- ALK7 is a significant component of TGF-beta superfamily signaling pathways, particularly in development.