Alternative titles; symbols
HGNC Approved Gene Symbol: FHL5
Cytogenetic location: 6q16.1 Genomic coordinates (GRCh38) : 6:96,562,574-96,618,626 (from NCBI)
ACT is a LIM-only protein that interacts with transcription factor CREM (123812) in postmeiotic male germ cells and enhances CREM-dependent transcription (Kotaja et al., 2004). LIM proteins are defined by the possession of a highly conserved double zinc finger motif called the LIM domain.
By performing a yeast 2-hybrid screen on a mouse testis cDNA expression library using the CREM activation domain as bait, Fimia et al. (1999) isolated a cDNA encoding Act (activator of CREM in testis), a LIM-only protein that specifically associates with CREM. The LIM domain is a cysteine-rich, double-zinc finger structural motif involved in protein-protein interactions. Act bypasses the classic requirements for CREM activation, namely phosphorylation of ser117 and interaction with CREB-binding protein (CREBBP; 600140). Northern blot analysis revealed that expression of Act is restricted to testis. Western blot analysis determined that Act colocalizes in purified spermatids with CREM.
Using the mouse sequence as query, Morgan and Whawell (2000) identified an EST containing ACT. The deduced 284-amino acid protein contains an N-terminal half-LIM domain followed by 4 LIM domains. ACT shares 58.5% identity with FHL2 (602633) and 85% identity with mouse Act. Northern blot analysis revealed moderate to high levels of expression in all squamous cell carcinoma, melanoma, and leukemia tumor cell lines tested. Using the mouse sequence to design primers, Palermo et al. (2001) cloned ACT by PCR and conventional screening of a testis cDNA library. The deduced 284-amino acid protein shares 88% homology with mouse Act. Western blot analysis of mouse and human testis revealed a single band of about 33 to 34 kD.
By deletion analysis of mouse Act, Fimia et al. (2000) determined that the activation function of Act depends on the specific arrangement of the LIM domains, which are essential for both transactivation and dimerization with wildtype Act sequences.
ACT is expressed exclusively in round spermatids, where it cooperates with transcriptional activator CREM in regulating various postmeiotic genes. Targeted inactivation of CREM leads to a complete block of mouse spermiogenesis. Macho et al. (2002) sought to identify the regulatory steps controlling the functional interplay between CREM and ACT. They found that ACT selectively associates with KIF17b (see 605037), a kinesin isoform highly expressed in male germ cells. The ACT-KIF17b interaction is restricted to specific stages of spermatogenesis and directly determines the intracellular localization of ACT. Sensitivity to leptomycin B indicates that KIF17b can be actively exported from the nucleus through the CRM1 receptor (602559). Thus, Macho et al. (2002) concluded that a kinesin directly controls the activity of a transcriptional coactivator by a tight regulation of its intracellular localization.
Morgan and Whawell (2000) identified 5 coding exons of the ACT gene spanning 13 kb. Palermo et al. (2001) determined that the ACT gene contains 6 exons. The first exon is untranslated.
By genomic sequence analysis, Morgan and Whawell (2000) mapped the FHL5 gene to chromosome 6q16.1-q16.3. By genomic sequence analysis and by FISH, Palermo et al. (2001) confirmed the assignment of the FHL5 gene to chromosome 6q16.1-q16.3.
To investigate the role of ACT in vivo, Kotaja et al. (2004) used gene targeting to generate Act-null mice by homologous recombination. Although the stages of spermatogenesis seemed phenotypically normal, mutant mice displayed a drastically decreased number of mature germ cells. In addition, a large proportion of the residual mature cells showed aberrations in tail and head morphology. These observations indicated that many genes whose function is crucial to the generation of mature germ cells are under the regulatory control of ACT. These genes were thought to represent a subset of the postmeiotic genes controlled by CREM. Kotaja et al. (2004) concluded that the fine tuning of sperm development is achieved by the coordinated action of 2 transcriptional regulators.
Fimia, G. M., De Cesare, D., Sassone-Corsi, P. A family of LIM-only transcriptional coactivators: tissue-specific expression and selective activation of CREB and CREM. Molec. Cell. Biol. 20: 8613-8622, 2000. [PubMed: 11046156] [Full Text: https://doi.org/10.1128/MCB.20.22.8613-8622.2000]
Fimia, G. M., De Cesare, D., Sassone-Corsi, P. CBP-independent activation of CREM and CREB by the LIM-only protein ACT. Nature 398: 165-169, 1999. [PubMed: 10086359] [Full Text: https://doi.org/10.1038/18237]
Kotaja, N., De Cesare, D., Macho, B., Monaco, L., Brancorsini, S., Goossens, E., Tournaye, H., Gansmuller, A., Sassone-Corsi, P. Abnormal sperm in mice with targeted deletion of the act (activator of cAMP-responsive element modulator in testis) gene. Proc. Nat. Acad. Sci. 101: 10620-10625, 2004. [PubMed: 15247423] [Full Text: https://doi.org/10.1073/pnas.0401947101]
Macho, B., Brancorsini, S., Fimia, G. M., Setou, M., Hirokawa, N., Sassone-Corsi, P. CREM-dependent transcription in male germ cells controlled by a kinesin. Science 298: 2388-2390, 2002. [PubMed: 12493914] [Full Text: https://doi.org/10.1126/science.1077265]
Morgan, M. J., Whawell, S. A. The structure of the human LIM protein ACT gene and its expression in tumor cell lines. Biochem. Biophys. Res. Commun. 273: 776-783, 2000. [PubMed: 10873680] [Full Text: https://doi.org/10.1006/bbrc.2000.3006]
Palermo, I., Litrico, L., Emmanuele, G., Giuffrida, V., Sassone-Corsi, P., De Cesare, D., Fimia, G. M., D'Agata, R., Calogero, A. E., Travali, S. Cloning and expression of activator of CREM in testis in human testicular tissue. Biochem. Biophys. Res. Commun. 283: 406-411, 2001. [PubMed: 11327716] [Full Text: https://doi.org/10.1006/bbrc.2001.4805]