Calcitonin RCAN1, also known as CSP1, Down syndrome key region protein 1 (DSC1), muscle cell enriched calcineurin interacting protein 1 (MCIP1), and Adapt78, is a member of the calcineurin regulator (RCAN) family, which has three members: RCAN1, RCAN2, and RCAN3. RCAN1 inhibits calcineurin-dependent transcriptional responses by binding to the catalytic domain of calcineurin A. It may play a role in the development of the central nervous system.
(Data source: Lee SK, et al. Mol Cells . 2020)
CSP1 expression distribution
CSP1 is expressed in various tissues of the human body, but it is enriched in specific organs. In the central nervous system, its expression is mainly concentrated in the cerebral cortex and hippocampus; it is highly expressed in cardiomyocytes and participates in the regulation of cardiac hypertrophy and heart failure; it is also expressed in the endocrine system such as the pancreas and adrenal glands.
(Data source: uniprot)
The structure of CSP1 and its receptor
CSP1 is a cytoplasmic protein located on human chromosome 21q22.12. The gene consists of seven exons and, through different mRNA splicing processes, generates two main transcripts, RCAN1.1 and RCAN1.4. RCAN1 contains a structured N-terminal RNA recognition motif (RRM) domain that binds to mRNA, and a C-terminal domain that binds to nucleotides (CNs). The C-terminal domain contains LxVP, SPPASPP, PxIxIT, and TxxP motifs that directly bind to CNs.
(Data source: Lao M , et al. Mol Med. 2022)
Calmodulin-dependent serine/threonine phosphatase (CN) is composed of a catalytic subunit, calmodulin A (CNA) , and a regulatory subunit, calmodulin B (CNB). It is present in various human tissues and regulates multiple biological processes through dephosphorylation, including immune responses, neural function, tumor metabolism, and sleep regulation. When RCAN1 approaches CN, its C-terminus undergoes a binding -folding conformational change. It folds to form a stable α-helix and β-sheet structure . RCAN1 utilizes the PxIxIT motif to bind to and block the substrate recruitment site of CN, while simultaneously using the TxxP motif to directly insert into the catalytic active site of CN, inhibiting its dephosphorylation activity.
(Data source: Li Y, et al. Sci Adv. 2020)
CSP1 signaling pathway in tumor progression
RCAN1 inhibits CN activity by blocking the LxVP and PxIxIT interaction groove, essential substrate recruitment sites for CN. The inhibitory effect of RCAN1 on CN can be weakened by phosphorylation of RCAN1. RCAN1 inhibits the CN-NFAT pathway and the transcription of NFAT-regulated genes, including IGF-1, VEGFA, ANG-2, IFI27, CXCL8, IL-8, and IL-11, thereby suppressing cancer cell proliferation and migration.
(Data source: Lao M, et al. Mol Med. 2022)
The role of CSP1 in other diseases
Because the RCAN1 gene is located on chromosome 21, the extra chromosome in patients with Down syndrome leads to its overexpression. This is considered one of the important molecular mechanisms underlying congenital heart disease and intellectual disability in Down syndrome patients. Abnormal accumulation of RCAN1 may lead to neurofibrillary tangles by inhibiting the dephosphorylation of Tau protein. Simultaneously, it upregulates the production of β-amyloid (Aβ), promoting the deposition of toxic plaques; the resulting synaptic dysfunction and mitochondrial damage exacerbate neuronal death, becoming a key pathological driver and therapeutic target in Alzheimer's disease (AD).
(Data source: Dohl J, et al. Alzheimers Dement. 2025)
CSP1 targeted therapy
AMI605 is a small molecule chemical drug targeting CSP1, developed by Amira Therapeutics for the treatment of glioblastoma, and is currently in the preclinical research stage.
(Data source: amiratx official website)
