Small but crucial : the novel small heat shock protein Hsp21 mediates stress adaptation and virulence in Candida albicans

Peer reviewedPublisher PD

The expression of HSP60 and HSP10 in large bowel carcinomas with lymph node metastase

BACKGROUND: The involvement of Heat Shock Proteins (HSP) in cancer development and progression is a widely debated topic. The objective of the present study was to evaluate the presence and expression of HSP60 and HSP10 in a series of large bowel carcinomas and locoregional lymph nodes with and without metastases. METHODS: 82 Astler and Coller's stage C2 colorectal cancers, of which 48 well-differentiated and 34 poorly-differentiated, were selected along with 661 lymph nodes, including 372 with metastases and 289 with reactive hyperplasia only, from the same tumours. Primitive tumours and both metastatic and reactive lymph nodes were studied; specifically, three different compartments of the lymph nodes, secondary follicle, paracortex and medullary sinus, were also analysed. An immunohistochemical research for HSP60 and HSP10 was performed and the semiquantitative results were analysed by statistical analysis to determine the correlation between HSPs expression and 1) tumour grading; 2) degree of inflammation; 3) number of lymph nodes involved; 4) lymph node compartment hyperplasia. Moreover, western blotting was performed on a smaller group of samples to confirm the immunohistochemical results. RESULTS: Our data show that the expression of HSP60, in both primary tumour and lymph node metastasis, is correlated with the tumoral grade, while the HSP10 expression is not. Nevertheless, the levels of HSP10 are commonly higher than the levels of HSP60. In addition, statistical analyses do not show any correlation between the degree of inflammation and the immunopositivity for both HSP60 and HSP10. Moreover, we find a significant correlation between the presence of lymph node metastases and the positivity for both HSP60 and HSP10. In particular, metastatic lymph nodes show a higher percentage of cells positive for both HSP60 and HSP10 in the secondary follicles, and for HSP10 in the medullary sinuses, when compared with hyperplastic lymph nodes. CONCLUSION: HSP60 and HSP10 may have diagnostic and prognostic significance in the management of this tumour and their overexpression in tumoral cells may be functionally related to tumoral progression. We hypothesise that their expression in follicular and medullary cells of lymph nodes may be induced by formation of metastases. Further studies based on these observations could lead to a better understanding of the HSPs involvement in colorectal cancer progression, as well as other neoplasms

Identification of in vivo substrates of the yeast mitochondrial chaperonins reveals overlapping but non-identical requirement for hsp60 and hsp10

The mechanism of chaperonin-assisted protein folding has been mostly analyzed in vitro using non-homologous substrate proteins. In order to understand the relative importance of hsp60 and hsp10 in the living cell, homologous substrate proteins need to be identified and analyzed. We have devised a novel screen to test the folding of a large variety of homologous substrates in the mitochondrial matrix in the absence or presence of functional hsp60 or hsp10. The identified substrates have an Mr of 15-90 kDa and fall into three groups: (i) proteins that require both hsp60 and hsp10 for correct folding; (ii) proteins that completely fail to fold after inactivation of hsp60 but are unaffected by the inactivation of hsp10; and (iii) newly imported hsp60 itself, which is more severely affected by inactivation of hsp10 than by inactivation of pre-existing hsp60. The majority of the identified substrates are group I proteins. For these, the lack of hsp60 function has a more pronounced effect than inactivation of hsp10. We suggest that homologous substrate proteins have differential chaperonin requirements, indicating that hsp60 and hsp10 do not always act as a single functional unit in vivo

Mol. Cell. Biol.

The majority of cytosolic proteins in eukaryotes contain a covalently linked acetyl moiety at their very N terminus. The mechanism by which the acetyl moiety is efficiently transferred to a large variety of nascent polypeptides is currently only poorly understood. Yeast N-acetyltransferase NatA, consisting of the known subunits Nat1p and the catalytically active Ard1p, recognizes a wide range of sequences and is thought to act cotranslationally. We found that NatA was quantitatively bound to ribosomes via Nat1p and contained a previously unrecognized third subunit, the N-acetyltransferase homologue Nat5p. Nat1p not only anchored Ard1p and Nat5p to the ribosome but also was in close proximity to nascent polypeptides, independent of whether they were substrates for N-acetylation or not. Besides Nat1p, NAC (nascent polypeptide-associated complex) and the Hsp70 homologue Ssb1/2p interact with a variety of nascent polypeptides on the yeast ribosome. A direct comparison revealed that Nat1p required longer nascent polypeptides for interaction than NAC and Ssb1/2p. nat1 or ard1 deletion strains were temperature sensitive and showed derepression of silent mating type loci while nat5 did not display any obvious phenotype. Temperature sensitivity and derepression of silent mating type loci caused by nat1 or ard1 were partially suppressed by overexpression of SSB1. The combination of data suggests that Nat1p presents the N termini of nascent polypeptides for acetylation and might serve additional roles during protein synthesis

Human Hepatitis B Virus Polymerase Interacts with the Molecular Chaperonin Hsp60

Previous studies showed that hepatitis B virus polymerase (HBV Pol) interacts with host factors such as the Hsp90 complex, which is a critical step in viral genome replication. In this report, we propose that another chaperone, Hsp60, interacts with human HBV Pol and that this is a very important step for maturation of human HBV Pol into the active state. In the immunoprecipitation of recombinant human HBV Pol expressed in insect cells with the recombinant baculovirus expression system, the 60-kDa protein was coimmunoprecipitated with Pol and the protein was identified as Hsp60 through peptide sequencing and immunogenic analysis with an anti-Hsp60 antibody. In vitro experiments showed that Hsp60 strongly affected human HBV Pol activity in that (i) blocking of Hsp60 by the protein-specific antibody reduced human HBV Pol activity, (ii) the activity was increased by addition of Hsp60 in the presence of ATP, and (iii) ATP synergistically activated human HBV Pol with Hsp60. In vivo experiments showed that inhibition of Hsp60 in cells by a mutant Hsp60, CΔ540, resulted in the reduction of human HBV Pol activity. In summary, our results indicate that the interaction is significant for conversion of human HBV Pol into the active state

Altered mechano-chemical environment in hip articular cartilage: effect of obesity

The production of extracellular matrix (ECM) components of articular cartilage is regulated, among other factors, by an intercellular signaling mechanism mediated by the interaction of cell surface receptors (CSR) with insulin-like growth factor-1 (IGF-1). In ECM, the presence of binding proteins (IGFBP) hinders IGF-1 delivery to CSR. It has been reported that levels of IGF-1 and IGFBP in obese population are, respectively, lower and higher than those found in normal population. In this study, an experimental-numerical approach was adopted to quantify the effect of this metabolic alteration found in obese population on the homeostasis of femoral hip cartilage. A new computational model, based on the mechano-electrochemical mixture theory, was developed to describe competitive binding kinetics of IGF-1 with IGFBP and CSR, and associated glycosaminoglycan (GAG) biosynthesis. Moreover, a gait analysis was carried out on obese and normal subjects to experimentally characterize mechanical loads on hip cartilage during walking. This information was deployed into the model to account for effects of physiologically relevant tissue deformation on GAG production in ECM. Numerical simulations were performed to compare GAG biosynthesis in femoral hip cartilage of normal and obese subjects. Results indicated that the lower ratio of IGF-1 to IGFBP found in obese population reduces cartilage GAG concentration up to 18 % when compared to normal population. Moreover, moderate physical activity, such as walking, has a modest beneficial effect on GAG production. The findings of this study suggest that IGF-1/IGFBP metabolic unbalance should be accounted for when considering the association of obesity with hip osteoarthritis