Cancer cells overexpress heat shock proteins (Hsps), the major components of cellular stress response, to overcome the diversity of stresses and to survive. However, the specific roles of Hsps in initiation and establishment of cancers remain unclear. Using loss of Lgl function-mediated epithelial tumorigenesis in Drosophila, we induced tumorigenic MARCM clones of different genetic backgrounds in wing imaginal discs to examine the temporal and spatial expression and roles of major heat shock proteins in tumor growth. The constitutively expressed Hsp83, Hsc70 (heat shock cognate), Hsp60 and Hsp27 show elevated levels in all cells of the tumorigenic clone since early stages, which persists till their transformation. However, the stressinducible Hsp70 is expressd only in a few cells at later stage of established tumorous clones that show high Factin aggregation. Intriguingly, levels of heat shock factor (HSF), the master regulator of Hsps, remain unaltered in these tumorous cells and its down-regulation does not affect tumorigenic growth of lglclones overexpressing Yorkie, although down-regulation of Hsp83 prevents their survival and growth. Interestingly, overexpression of HSF or Hsp83 in lglcells makes them competitively successful in establishing tumorous clones. These results show that the major constitutively expressed Hsps, but not the stress-inducible Hsp70, are involved in early as well as late stages of epithelial tumors and their elevated expression in lglclones co-overexpressing Yorkie is independent of HSF.

Cancer cells overexpress heat shock proteins (Hsps), the major components of cellular stress response, to overcome the diversity of stresses and to survive. However, the specific roles of Hsps in initiation and establishment of cancers remain unclear. Using loss of Lgl function-mediated epithelial tumorigenesis in Drosophila , we induced tumorigenic MARCM clones of different genetic backgrounds in wing imaginal discs to examine the temporal and spatial expression and roles of major heat shock proteins in tumor growth. The constitutively expressed Hsp83, Hsc70 (heat shock cognate), Hsp60 and Hsp27 show elevated levels in all cells of the tumorigenic clone since early stages, which persists till their transformation. However, the stressinducible Hsp70 is expressd only in a few cells at later stage of established tumorous clones that show high Factin aggregation. Intriguingly, levels of heat shock factor (HSF), the master regulator of Hsps, remain unaltered in these tumorous cells and its down-regulation does not affect tumorigenic growth of lgl - clones overexpressing Yorkie, although down-regulation of Hsp83 prevents their survival and growth. Interestingly, overexpression of HSF or Hsp83 in lgl - cells makes them competitively successful in establishing tumorous clones. These results show that the major constitutively expressed Hsps, but not the stress-inducible Hsp70, are involved in early as well as late stages of epithelial tumors and their elevated expression in lgl - clones co-overexpressing Yorkie is independent of HSF.

Oncogenic cells recruit diverse cellular survival machineries, including the highly conserved heat shock proteins (Hsps), to counter stressful conditions during tumour progression. Despite important roles of Hsps in several cancers, poor understanding of their regulation leaves major gaps in identifying mechanisms of cellular stress responses exploited by cancer cells. Following our earlier report of stress inducible Hsp70 expression only in a few cells in polarity defective tumorous clones, we now show that Hsp70 is expressed only in neoplastic tumours. Hsp70 expression at 72h after clone induction is mostly limited to a few lgl- ykiOE cells exhibiting mesenchymal features in hypoxic zone closer to tracheae, although all tumorous cells express hsp70 transcripts. Down-regulation of the hsp70a but not hsp70b cluster transcripts substantially suppresses growth of lgl- ykiOE clones without affecting their early establishment. However, over-expression of Hsp70 or Hsp70-cochaperone DnaJ suppress lgl- ykiOE clones growth at early stage. This spatially and temporally regulated expression of Hsp70 in lgl- ykiOE clones is independent of HSF but requires dFOXO and JNK signalling, while a nearly similar pattern of Hsp70 expression in lgl- RasV12 clones requires HSF, rather than dFOXO. Such context dependent Hsp70 regulation provides novel insight into stress regulatory machinery in cancer cells.

Cancer cells experience a variety of stresses like hypoxia, lack of nutrients, DNA damage and immune responses, which trigger several processes to drive genomic instability and mutation, alterations in gene expression programs, and reprogramming of the metabolic pathways to escape growth inhibition signaling, and acquire resistance to the immune surveillance. Different heat shock proteins are expressed at elevated levels in cancer cells. However, their specific roles in initiation, establishment and progression of cancers are still not clear. Here using the loss of function allele of the apico-basal polarity gene, lgl, we have established models for induction of tumorous somatic clones of different genetic constitutions at defined developmental times for examination of temporal and spatial patterns of expression of the major heat shock protein families, namely Hsp83, Hsp70, Hsp60 and Hsp27. The Hsp83, Hsp60 and Hsp27 begin to express in all cells of the tumor at high levels since early stages (48hr after tumor induction) and continue their high expression at later stages when the tumorous clones accumulate F-actin and get transformed. Levels of the heat shock cognate Hsc70 proteins also follow the same pattern as the other Hsps. However, the major stress-inducible Hsp70 is not expressed at early stages of tumor growth, but expresses at a later stage only in a few cells in a given lgl loss of function clone, which also shows high F-actin aggregates. Thus, the major Hsps, except the Hsp70, seems to be involved in early as well as late stages of epithelial tumors induced by loss of the Lgl cell polarity protein, while the Hsp70 expression in a few cells coincides with their getting transformed. This model will be useful for further genetic studies to dissect specific roles of different Hsps in tumor development and their therapeutic manipulation.