, Volume 11, Issue 1, pp 23–33 | Cite as

Synaptophysin-containing microvesicles transport heat-shock protein hsp60 in insulin-secreting beta cells

  • Katrina Brudzynski
  • Violetta Martinez


58–62 kDa heat-shock proteins (hsp60) are molecular chaperonins involved in the process of protein folding, transmembrane translocation and assembly of oligomeric protein complexes. In eukaryotic cells hsp60 proteins have been found in mitochondria and chloroplasts. However, we have recently documented that, in addition to mitochondria, a hsp60-like protein is present in secretory granules of insulin-secreting beta cells. The pathway by which hsp60 is targeted to secretory granules was unknown. Here we report the existence of microvesicles involved in the transport of hsp60 protein. Immunoelectron microscopy of serial thin-sections of beta cells directly visualized stages associated with hsp60 delivery: attachment of microvesicles to a secretory granule, fusion with the secretory granule membrane and release of hsp60 molecules. Further biochemical and immunological analysis of microvesicles revealed the presence in their membrane of synaptophysin, a major component of synaptic-like microvesicles (SLMV) of neuroendocrine cells. Double immunogold labelling with antibodies to synaptophysin and hsp60 demonstrated co-localization of both proteins in the same microvesicles. Moreover, fusion of synaptophysin-positive microvesicles leaves synaptophysin incorporated, at least transiently, to secretory granule membranes. These findings suggest that, in beta cells, synaptic-like vesicles are involved in the transport and delivery of hsp60 and represent a novel pathway for protein transport and secretion.

Key words

hsp60 protein islet beta cells protein transport synaptophysin synaptic-like microvesicles 


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Copyright information

© Kluwer Academic Publishers 1993

Authors and Affiliations

  • Katrina Brudzynski
    • 1
  • Violetta Martinez
    • 2
  1. 1.Robarts Research InstituteUniversity of Western OntarioLondonCanada
  2. 2.Department of Pathology, University HospitalUniversity of Western OntarioLondonCanada

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