Loss of E-cadherin in the vicinity of necrosis in colorectal carcinomas: association with NFkappaB expression.

The transcription factor NFkappaB regulates the expression of several tumor-related molecules associated with tumor progression and metastasis. However, the precise mechanisms by which its activation mediates these processes in diverse tumors are unknown. In this study we determined the expression of NFkappaB in various colorectal carcinoma cell lines, in a series of 90 non-metastatic and metastatic colorectal tumors and in an in vitro 3D-spheroid model of HT-29 cells simulating morphological hallmark of these adenocarcinomas, namely neoplastic glandular nests around a necrotic center. We show that the inactive cytoplasmic NFkappaB form is evidently up-regulated in the tumor epithelium, especially in the metastatic cases, as compared to normal tissue. We found that in situ nuclear NFkappaB staining is characteristic for cells that are still viable but dissociated from the surrounding cohesive tumor tissue and destined to die. Evidence for a possible association between NFkappaB expression and loss of cell adhesion mediated by E-cadherin function has been provided in vivo and in vitro using the HT-29 3D-spheroid model. In both cases, we found a strong correlation between activation of NFkappaB and loss of E-cadherin expression. Considering the fact that cancer cell necrosis plays a crucial role in metastasis, NFkappaB activation mediated by loss of E-cadherin may represent an essential, even initial event in this process. Furthermore, we present in vitro data implicating LPS, the endotoxin of gram-negative bacteria, in the triggering of NFkappaB up-regulation. Thus, release of bacterial endotoxin may essentially contribute to the progression of colon cancer in vivo.