Disease relevance of Hspa2

• Targeted gene disruption of Hsp70-2 results in failed meiosis, germ cell apoptosis, and male infertility [1].
• In the development of mouse models deficient in the breast cancer susceptibility gene 2 (Brca2) or the 70-kd heat shock protein (Hsp70-2), 3-4-week-old chimeras developed single or multiple masses composed of both well-differentiated and poorly differentiated tissues derived from all three germ layers [2].
• Remarkably, ectopic LEDGF also increases the tumorigenic potential of human cancer cells in immunodeficient mice, and LEDGF expression is increased in human breast and bladder carcinomas correlating with that of Hsp70-2 in invasive bladder cancer [3].

High impact information on Hspa2

• Furthermore, analysis of nuclei and genomic DNA indicated that the failure of meiosis in Hsp70-2 -/- mice was coincident with a dramatic increase in spermatocyte apoptosis [1].
• Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile [1].
• While synaptonemal complexes assembled in Hsp70-2 -/- spermatocytes, structural abnormalities became apparent in these cells by late prophase, and development rarely progressed to the meiotic divisions [1].
• Metaphase spermatocytes were not seen in tissue sections from testes of Hsp70-2(-/-) mice, and expression of mRNAs and antigens characteristic of late pachytene spermatocytes (e.g., cyclin A1) and development of spermatids did not occur [4].
• Spermatogenesis in homozygous mutant mice (Hsp70-2[-/-]) proceeded normally until day 15 when increasing numbers of pachytene spermatocytes became apoptotic and differentiation of cells beyond the pachytene stage began to falter [4].

Biological context of Hspa2

• However, neither meiosis nor fertility was affected in female Hsp70-2 -/- mice [1].
• Spermatogenic cells synthesize a unique 70-kDa heat shock protein (HSP70-2) during prophase of meiosis I, and targeted disruption of the Hsp70-2 gene has shown that this protein is required for spermatogenic cell differentiation in adult mice [4].
• The present study examined the occurrence of apoptotic cell death in the testis of wild-type mice from postnatal days 3 to 26 and in juvenile Hsp 70-2 knockout mice [5].
• Analysis of the sequence indicates that HSPA2 is the human homologue of the murine Hsp70-2 gene with 91.7% identity in the nucleotide coding sequence and 98.2% in the corresponding amino acid sequence [6].
• Meiotic metaphase I and II chromosome spreads were observed in spermatogenic cells from Hsp70-2(-/-) mice but at a much lower frequency than in wild-type mice [7].

Anatomical context of Hspa2

• However, cells with a putative acrosome were present occasionally in histological sections of the testes of juvenile and adult Hsp70-2(-/-) mice [7].
• Adult Hsp 70-2 knockout males are infertile and lack spermatids and spermatozoa (Dix et al. [1996a] Proc. Natl. Acad. Sci. U.S.A. 93:3264-3268) [5].
• The expression of hsp70.2, an hsp70 gene family member, originally characterized by its high levels of expression in germ cells in the adult mouse testis, was detected in several other reproductive tissues, including epididymis, prostate, and seminal vesicles, as well as in extraembryonic tissues of mid-gestation fetuses [8].
• We have examined the spatial pattern of expression of a member of the hsp70 gene family, hsp70.2, in the mouse central nervous system [9].
• RNA blot analysis revealed low levels of the 2.7 kb transcript of hsp70.2 in several areas of the brain, with highest signal in the hippocampus [9].

Associations of Hspa2 with chemical compounds

• Propidium iodide staining and cytophotometry indicated that the average DNA content of nuclei in MN7-positive cells in Hsp70-2(-/-) mice was usually about twice, or occasionally the same as, that of nuclei in round spermatids of wild-type mice [7].
• Here we have shown that sequences proximal to the exon1/intron splicing site in the 5' untranslated region of the Hsp70.2/Hst70 gene, which include a highly conserved element called box B, are required for efficient expression of the chloramphenicol acetyltransferase reporter gene in testes of transgenic mice [10].

Physical interactions of Hspa2

• MSJ-1 is able to interact with the testis-specific Hsp70-2 protein and can be coimmunoprecipitated with Hsp70-2 from spermatogenic cells; binding of these two chaperones is consistent with the presence of a third component, which is so far unknown [11].
• We further demonstrate that the constitutive HSF2 DNA-binding activity present in testis is able to interact with promoter sequences of the hsp70.2 gene, a testis-specific member of the hsp70 gene family [12].

Other interactions of Hspa2

• Two additional genes encode proteins that are developmentally regulated and expressed specifically in spermatogenic cells (Hsp70-2, Hsc70t) [13].
• The rat Hst70 gene and its mouse counterpart Hsp70.2 belong to the family of Hsp70 heat shock genes and are specifically expressed in male germ cells [14].
• Similar analysis also confirmed the initial Hsp70-2 assignment to Chr 12 with the order: Hsp70-2-Aat-Igh [15].
• Hsp70-2, which is known to be highly expressed in meiotic cells, shows a subcellular localization in late differentiating spermatids that overlaps that of MSJ-1 [11].
• We have now identified this protein as the testis-expressed 70-kDa heat shock protein chaperone known as HspA2 (the human homologue of mouse Hsp70-2) [16].

Analytical, diagnostic and therapeutic context of Hspa2

• To determine if this unique stress protein has a critical role in meiosis, we used gene-targeting techniques to disrupt Hsp70-2 in mice [1].
• Histochemistry with the periodic acid-Schiff procedure and immunostaining with monoclonal antibody MN7 verified that acrosomes were present in Hsp70-2(-/-) mice, and electron microscopy showed that some of these cells had condensing nuclei characteristic of step 8-9 spermatids [7].
• To better understand the genetic regulation of Hsp70-2, we used mRNA primer- extension, reverse transcriptase PCR (RT-PCR), and cDNA sequencing to determine that transcription began as far as 353 bp upstream of the start codon [17].
• Reverse-transcriptase-polymerase chain reaction (RT-PCR) analyses of gene expression confirmed this sex specificity; Hsp70-2 mRNA was detected in mouse testes, but not ovaries [18].
• Surprisingly, RNA blot analysis and in situ hybridization revealed abundant expression of an 'antisense' hsp70.2 transcript in several areas of adult mouse brain [9].

References