HSPA8

What is HSPA8?

Heat shock cognate protein 70 (HSC70), also known as HSP73, is a heat shock homologous protein with molecular weight of 73kDa. It is a constitutively expressed molecular chaperone encoded by HSPA8 gene.

Unlike HSP70, HSC70 can be expressed in the absence of any stress, mainly located in the cytoplasm and nucleolus.

As a chaperone, HSC70 can provide a variety of housekeeping functions. It can regulate the folding, transport, migration and collection of proteins, especially to help the refolding of misfolded proteins, so that the function of proteins can return to normal. In addition, it participates in the inflammatory signaling pathway through extracellular interaction with TLR2/TLR4.

The Structure of HSPA8

The HSC70 gene contains 8 introns, and its cDNA sequence has been found in human, rat, mouse, Chinese hamster and cattle cells. It is speculated that the protein encoded by the gene contains about 646 amino acids and the predicted molecular weight is about 73 kDa.

The basic structure of human HSC70 consists of three parts:

44kDa N-terminal adenosine triphosphatase (ATPase) domain (AA 1 - 384), also known as ATP binding domain.

18kDa polypeptide (substrate) binding domain (AA 385 - 543).

10kDa carboxyl terminal domain (AA 544 - 646).

Carboxyl terminal amino acid sequence Glu-Glu-Val-Asp (EEVD motif) is highly conserved in HSC70 and HSP70 of all eukaryotes and plays an important role in association with some molecular chaperones. This conserved motif is beneficial to the binding of HSC70 and HSP70 to other chaperone molecules. The terminal amino acid sequence is specific in different organelles, such as EEVD, in the cytoplasm, HDEL, in the endoplasmic reticulum, PEAEYEEAKK, in the mitochondria and PECDVLDADFTDFTDSK in the plastids.

The Expression of HSPA8

HSC70 exists in all prokaryotes and eukaryotes, and shows basic expression in normal cells, thus maintaining the basic morphology and function of cells. Under the stimulation of environmental stress factors (such as high temperature, heavy metals and microbial infection, etc.), its expression increased significantly.

HSC70 is highly expressed in the nervous system, and its expression changes in time and space with the development of the nervous system, suggesting that it is involved in neural development.

Compared with normal cell lines, the expression of HSC70 is higher in some cancer cell lines. Compared with normal mucosal epithelial cells, HSC70 was highly expressed in cervical squamous cell carcinoma and vaginal squamous cell carcinoma. The expression of HSC70 in colon cancer tissues was significantly higher than that in adjacent normal tissues. The expression of HSC70 in esophageal squamous cell carcinoma was also significantly increased.

The Function of HSPA8

HSC70 is fundamentally expressed in normal cells and plays a role in the normal metabolism and physiological regulation of cells.

HSC70 is an important cytoplasmic molecular chaperone protective protein, which is widely involved in a variety of functions to protect the body and cells, enhance the body's stress tolerance and improve cell survival.

As a molecular chaperone, it is involved in a variety of cellular processes, including the folding of new peptides, protein transmembrane transport, proteolysis activation of misfolded proteins, and the formation and dissociation of protein complexes.

In addition to chaperone function, secreted HSC70 also participates in inflammatory signaling pathway through extracellular interaction with TLR2/TLR4. During nutritional stress, it also plays a central role in regulating intracellular antigen transport to control MHC class II presentation. In addition, HSC70 may act as a molecular switch to regulate endocytosis and autophagy.

HSC70 is highly expressed in mammalian nervous system and neuronal cell bodies, and temporal and spatial regulation occurs with the development of nervous system, indicating that it is involved in neural development.

It has been found that HSC70 can mediate the infection and release of hepatitis C virus (HCV) particles, and it is also an important helper protein for HBV replication. The role of heat shock proteins in virus replication provides a new idea for the research of antiviral drugs.

HSC70 plays an important role in the initiation of labor.

The important function of HSC70 also makes it closely related to a variety of diseases.

HSC70 plays an important role in regulating the innate immune response of ischemia-reperfusion myocardium and protecting cardiac function. In addition, HSC70 plays an important role in neurological diseases, liver diseases, breast cancer and other cancers.

The Latest Research Progress

Research shows miR-26b-5p imparts metastatic properties and helps in maintenance of Ep CSCs via HSC70. Thus, miR-26b-5p and HSC70 could serve as molecular targets for selectively eliminating the Ep CSC population in human HCCs.

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