Comparative Immunohistochemical Analysis of Ochratoxin A Tumourigenesis in Rats and Urinary Tract Carcinoma in Humans; Mechanistic Significance of p-S6 Ribosomal Protein Expression

Patrycja Gazinska,Cheryl Gillett,Sarah Pinder,Peter Mantle,Diana Herman

doi:10.3390/toxins4090643

Patrycja Gazinska, Cheryl Gillett + Show 3 more

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https://doi.org/10.3390/toxins4090643

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Abstract

Ochratoxin A (OTA) is considered to be a possible human urinary tract carcinogen, based largely on a rat model, but no molecular genetic changes in the rat carcinomas have yet been defined. The phosphorylated-S6 ribosomal protein is a marker indicating activity of the mammalian target of rapamycin, which is a serine/threonine kinase with a key role in protein biosynthesis, cell proliferation, transcription, cellular metabolism and apoptosis, while being functionally deregulated in cancer. To assess p-S6 expression we performed immunohistochemistry on formalin-fixed and paraffin-embedded tumours and normal tissues. Marked intensity of p-S6 expression was observed in highly proliferative regions of rat renal carcinomas and a rare angiosarcoma, all of which were attributed to prolonged exposure to dietary OTA. Only very small OTA-generated renal adenomas were negative for p-S6. Examples of rat subcutaneous fibrosarcoma and testicular seminoma, as well as of normal renal tissue, showed no or very weak positive staining. In contrast to the animal model, human renal cell carcinoma, upper urinary tract transitional cell carcinoma from cases of Balkan endemic nephropathy, and a human angiosarcoma were negative for p-S6. The combined findings are reminiscent of constitutive changes in the rat tuberous sclerosis gene complex in the Eker strain correlated with renal neoplasms, Therefore rat renal carcinogenesis caused by OTA does not obviously mimic human urinary tract tumourigenesis.

Highlights

Ochratoxin A is well known as one of the first mycotoxins to be discovered in the 1960s, later shown to be responsible for chronic nephropathy in commercial pig production [1], and as generally toxic in experimental animals [2]
Since inactivation of the Tsc2 and folliculin genes in mice have been associated with the development of renal tumours and mammalian target of rapamycin disregulation [14], we investigated the Ochratoxin A (OTA)-associated tumours for evidence of mTOR activation
Phospho-S6 ribosomal protein was consistently expressed in rat renal carcinomas and adenocarcinomas in response to long-term exposure to dietary OTA, in contrast to its absence from adjacent uninvolved kidney and other natural tumours

Summary

Introduction

Ochratoxin A is well known as one of the first mycotoxins to be discovered in the 1960s, later shown to be responsible for chronic nephropathy in commercial pig production [1], and as generally toxic in experimental animals [2]. Its specific significance arose when it was shown to be a potent renal carcinogen in male rats after protracted exposure via oral gavage, which was generally well tolerated [3,4]. Feeding studies with male mice extended the range of OTA carcinogenicity [5] and in subsequent rat carcinogenesis studies the toxin was homogenised into diet [6]. It is possible that the wide sensitivity of animals to the toxin shown in experimental toxicology can be extended to man, but this remains unclear [2]. The fact that most human renal carcinoma remains idiopathic [7] leaves ample room for hypothetical aetiologies

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