Heat shock cognate 70 protein secretion as a new growth arrest signal for cancer cells

Abstract

Earlier studies indicated that density-arrested cancer cells released an unidentified growth inhibitor whose secretion was prevented by overexpression of the lysosomal protease cathepsin D (cath D). In this study, this growth inhibitor was purified by affinity chromatography and identified as the heat shock cognate 70 protein (hsc70) based on its peptide microsequencing and specific antibody recognition. Among intracellular proteins, including other heat shock proteins, only constitutive hsc70 was secreted in response to the high-cell density. Moreover, hsc70 secretion from cancer cells was generated by serum deprivation, whereas its cellular concentration did not change. Prevention of Hsc70 secretion by cath D overexpression was associated with the formation of multilayer cell cultures, thus indicating a loss of contact inhibition. In addition, we showed that supplementing the culture medium with purified hsc70 inhibited cell proliferation in the nanomolar range. Conversely, removal of this extracellular hsc70 from the medium by either retention on ADP-agarose or competition at the Hsc70 binding site restored cell proliferation. Hsc70 appears active in human breast cancer cells and hypersecreted by direct cath D inhibition. These results suggest a new role of this secreted hsc70 chaperone in cell proliferation that might account for the higher tumor growth of cancer cells overexpressing cath D.

Heat shock cognate protein 70 isoform D is required for clathrin-dependent endocytosis of Japanese encephalitis virus in C6/36 cells

“…Despite its similarity across many taxa, Hsc70 is diverse in its functions (Takei & Haucke, 2001;Zhao et al, 2009). In the mosquito Aedes aegypti, Hsc70 isoform B is differentially expressed in response to treatment with heat shock (Nirdé et al, 2010); however, it was identified in an immune response-activated haemocyte library derived from the mosquito Armigeres subalbatus (Bartholomay et al, 2004). The increased expression of Hsc70 has also been shown in Anopheles gambiae when infected by the o'nyong-nyong virus (ONNV) (Sim et al, 2005).…”

HSPA8/HSC70 chaperone protein

“…147,148 It is worth mentioning that besides its intracellular location, HSPA8 is also detected in the extracellular space. It may derive from dying cells, but can also be actively released from intact cells, either free [149][150][151] or associated with exosomes. 152 Extracellular HSPA8 inhibits tumor cell growth 151 and modifies cell viability.…”

“…It may derive from dying cells, but can also be actively released from intact cells, either free [149][150][151] or associated with exosomes. 152 Extracellular HSPA8 inhibits tumor cell growth 151 and modifies cell viability. This property still remains a matter of debate since both proapoptotic and anti-apoptotic effects are observed.…”

Modulation of the ovarian cancer humoral response by tumor-derived exosomes.

“…Subsequent studies of these cells revealed that this overexpression prevented the release of HSC70, which led to the malignant phenotype [229]. immunosurveillance.…”

“…Additionally, it can catalyze the disassembly of clathrin cages [227] and has been implicated in the regulation of tumorigenesis and apoptosis [228]. With the assistance of co-chaperones, HSC70 can be recruited to the intracellular membrane [227], but can be released from cells as a result of active secretion [229]. Humoral autoimmune reactions against HSC70 have been documented in patients with cancer-associated retinopathy (characterized by visual loss and impairment) an ocular manifestation of underlying cancer, generally small-cell lung carcinoma [230].…”