Tight junctions (zonulae occludentes, ZO) are cellularly regulated dynamic structures sensitive to envi- ronmental stress agents including ionizing radiation. Radiation induced pathological alterations of the small intestine (gastrointestinal radiation syndrome) are related to altered ZO-mediated paracellular transport. We carried out a quantitative morphological evaluation of the murine jejunal epithelial tight junctional structure in freeze fracture replicas as changed upon whole body X-ray irradiation and low energy microwave exposition. X-ray treatment (4 Gy, 1, 24 h) brought about a partial dearrangement of the ZO strand network which regenerated only partially by 24 h. This observation is in line with data on paracellular permeability increases and ZO-bound calcium drop caused by X-ray irradiation. On the other hand, microwave treatment (16 Hz-modulated 2.45 GHz wave, 1 mW/cm 2 power density, 1 h exposition, samples at 1 and 3 h after exposition) did not cause dearrangement but, rather an increase in the integra- tion of thight junctional structure, which is in agreement with an increase in cytochemically detectable ZO-bound calcium.
Although angiogenesis is considered to be indispensable for continuous tumour growth, only very few studies have been published performing microvessel quantification during tumour progression. We mea- sured the tumour vascularity in different stages of rat pancreatic carcinogenesis induced by azaserine and promoted by raw soya flour-containing pancreatotrophic diet. Besides the tumour samples taken at 6 (atypical acinar cell nodules), 15 (adenomas) and 20 (localised adenocarcinomas) months after carcino- gen initiation, we also investigated 3 control groups: tumour-bearing host tissue of azaserine-treated rats and normal tissue of untreated rats kept on standard or pancreatotrophic diet. In contrast with the usual microvessel counting on hot spots, we determined microvascular surface density (SV) and volume den- sity (VV) by electron microscopic morphometry. There was no significant difference in these respect between the control groups. At month 6 after the azaserine induction SV and VV showed slight, non- significant decrease as compared to the host control. Both values remained unchanged until the 15th month and increased significantly by the 20th month. These results may indicate comparable growth rate of tumour and new microvessels in the premalignant stages of carcinogenesis while a more intense angio- genesis than tumour growth afterwards.
The ubiquitin (Ub)- proteasome proteolytic system is highly selective, and the specific proteins involved in cell division, growth, activation, signaling and transcription are degraded at different rate depending on the physio-pathological state of the cell. Ubiquitination serves first of all as a signal for protein degra- dation of short-lived and abnormal proteins under several stressful conditions. The immunocytochemical localization of Ub in some malignant tumours has recently been presented and differences in Ub expres- sion has been observed during malignant transformation. Change in the level of Ub and Ub-conjugated proteins might reflect a higher metabolic-catabolic ratio in neoplastic cells. Most studies have been focused on the malignant stage of tumour progression, and only a few papers have dealt with the change in Ub and Ub-protein conjugates level during the whole progression. To address this problem, we applied an azaserine-induced pancreatic carcinogenesis model, in which premalignant and malignant stages were investigated throughout the progression. The level of Ub immunoreactivity was measured in nucleus and cytoplasm by electron microscopic immunocytochemical and morphometrical methods. We found a sig- nificant increase of Ub level in the nucleus and the cytoplasmic area in premalignant atypical acinar cell nodule (AACN) cells and in malignant adenocarcinoma in situ (CIS) cells at month 20 after initiation.
Authors:Krisztina Nagy, S. Tóth, Z. Pálfia and G. Réz
Growth regulation is a crucial event in tumour progression. Surprisingly, relatively few papers have dealt with the catabolic side of regulation, and there are practically no data regarding the autophagic process during tumour development. We approach this problem by morphometrical investigation into the possi- ble changes of autophagic activity during the progression of rat pancreatic adenocarcinoma induced by azaserine. In the present study, autophagic capacity of the azaserine-induced premalignant and malignant cells were characterised and compared to the respective host tissue cells of the rat pancreas and to the acinar cells in other stages of tumour development. Using vinblastine (VBL) as an enhancer, and cyclo- heximide (CHI) as an inhibitor of autophagic segregation we observed that autophagic capacity of pre- malignant cells (month 6 and 10 after initiation) is much higher than in the host tissue cells. We found a sharp decrease in self-digesting capacity in adenocarcinoma cells (month 20) where VBL induced a min- imal accumulation of autophagic vacuoles which was, surprisingly, not inhibited by CHI, i.e. the CHI- sensitive regulatory step was lost. The changes in autophagic capacity are probably associated to specif- ic steps of tumour progression in our system.