Transformation of immortalized colorectal crypt cells by microcystin involving constitutive activation of Akt and MAPK cascade

Abstract

It has been shown by epidemiological and animal studies that microcystin is an important exogenous factor involved in the carcinogenesis of colorectal cancer (CRC). However, details of the mechanism remain unclear. Transformation of colorectal cells is an important initial step in carcinogenesis. Whether microcystin is capable of transforming immortalized colorectal crypt cells, and what the mechanism might be, was investigated. In the present study, we demonstrated that immortalized colorectal crypt cells could be transformed by microcystin. Transformed colorectal crypt cells showed an anchorage-independent growth phenotype, and the proliferation activities of microcystin-transformed cells were also greater than that of immortalized colorectal crypt cells. The Akt and the p38, JNK of mitogen-activated protein kinase (MAPK) pathways in microcystin-transformed cells were found to be constitutively activated. In microcystin-transformed cells, PI3K, MAPKAPK2, Akt, cyclin D1 and cyclin D3 in the Akt pathway; IQGAP-2, RabGTPase, Rap1GAP, RasGAP, R-Ras, Krev-1 and TC21 of the Ras GTP/GDP protein family; and A-Raf, B-Raf and PAK in the Ras/MAPK pathway were all markedly upregulated. However, in positive control cells, dimethylhydrazine-transformed cells, only the Akt pathway was activated by PI3K, and no evidence of alteration of any molecules of the Ras superfamily was observed. Inhibition of Akt, p38 and JNK activation led to a reduced proliferation of microcystin-transformed cells. This implies that the constitutive activation of Akt and the p38, JNK of MAPK pathways in microcystin-transformed cells may be the mechanism by which this important external factor acts in the carcinogenesis of CRC.

Microcystin-LR activates the ERK1/2 kinases and stimulates the proliferation of the monkey kidney-derived cell line Vero-E6

“…Since the transformation of colorectal cells is an important initial step in carcinogenesis (Zhu et al, 2005), these results support the hypothesis of MCLR being a risk factor of colorectal cancer (Zhou et al, 2002). In the same study, it was also demonstrated that members of the Ras and Raf families were activated, but without further activation of ERK1/2 kinases (Zhu et al, 2005). Here we found in Vero-E6 cells that low MCLR concentration affected the ERK1/2 but not the p38 and JNK MAPK pathways.…”

“…A study from Zhu et al (2005) demonstrated that MCLR (0.1 nM) is able to transform immortalized colorectal crypt cells (NCC), rendering them anchorage independent and highly proliferative through the activation of the Akt and the p38 and JNK MAPK pathways. Since the transformation of colorectal cells is an important initial step in carcinogenesis (Zhu et al, 2005), these results support the hypothesis of MCLR being a risk factor of colorectal cancer (Zhou et al, 2002). In the same study, it was also demonstrated that members of the Ras and Raf families were activated, but without further activation of ERK1/2 kinases (Zhu et al, 2005).…”

“…This induces expression of cyclin D and promotes cell cycle progression (Chang and Karin, 2001;Fang and Richardson, 2005;Meloche and Pouysségur, 2007). Zhu et al (2005) have demonstrated that MCLR induces the transformation of immortalized colorectal crypt cells through the constitutive activation of AKT and MAPK (p38 and JNK) cascades. This supports the hypothesis that MCLR represents a risk of colorectal cancer because cellular transformation is an initial step of carcinogenesis (Zhu et al, 2005).…”

“…Zhu et al (2005) have demonstrated that MCLR induces the transformation of immortalized colorectal crypt cells through the constitutive activation of AKT and MAPK (p38 and JNK) cascades. This supports the hypothesis that MCLR represents a risk of colorectal cancer because cellular transformation is an initial step of carcinogenesis (Zhu et al, 2005). They also found that MCLR activates Ras and Raf, but without further effect on ERK1/2 status.…”

A review of reproductive toxicity of microcystins

“…Recent reports suggest that MCs modulate PPs activity not only by the direct inhibition of enzyme activity, but also through the regulation of protein expression [16][17][18][19][94][95][96][97]. PP1 and PP2A inhibition induces the disruption of the dynamic equilibrium of protein phosphorylation/dephosphorylation, leading to the damage of numerous cellular processes such as cytoskeleton organization, Wnt, Akt, p38, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2) of mitogen-activated protein kinase (MAPK) signaling pathways, metabolism and cell cycle [20,[98][99][100][101] (Fig. 4).…”