Activation of Akt/GSK3β and Akt/Bcl-2 signaling pathways in nickel-transformed BEAS-2B cells

Abstract

Abstract. The Akt signaling pathway has been implicated in a wide range of cellular functions involving cell survival and proliferation, angiogenesis, metabolism and cell migration. Accumulating evidence suggests that Akt perturbations play an important role in human malignancy. Here, we investigated Akt perturbation in nickel-transformed cells. Chronic treatment of human bronchial epithelial BEAS-2B cells with low doses of nickel chloride resulted in cell transformation demonstrated by anchorage-independent (AI) growth, increased cell growth and alterations of cell growth pattern. Western blot assays show that phosphorylation of Akt at Ser473, but not that of p38, JNK and ERK, was increased in nickel-transformed cells compared with controls. Inhibition of Akt or PI3K by pharmacological or biochemical interference suppressed nickel AI growth and cell growth of transformed cells. Activation of Akt led to inhibition of GSK3β by phosphorylation at Ser9 in nickel-transformed cells. In addition, two major anti-apoptotic proteins of the Bcl family, Bcl-2 and Bcl-XL, were increased in nickel-transformed cells. By employing the small interfering RNA technique (siRNA), our results showed that siRNA Akt attenuated the expression of Bcl-2 and Bcl-XL in nickel-transformed cells, indicating that induction of Bcl-2 and Bcl-XL was likely mediated through Akt. ROS generation was decreased in nickel-transformed cells compared with controls. Moreover, down-regulation of retinoblastoma protein (Rb) was observed in nickel-transformed cells. Taken together, these findings demonstrate that activation of Akt, followed by GSK3β inhibition and Bcl-2, Bcl-XL up-regulation and decrease of ROS generation, along with a synergistic effect of Rb down-regulation may cause apoptosis resistance, contributing to the overall mechanism of nickel carcinogenesis.

Elucidating the mechanisms of nickel compound uptake: A review of particulate and nano-nickel endocytosis and toxicity

“…Thus, at short exposure times the level of uptake is directly related to the level of transformation in SHE where crystalline Ni compounds all demonstrate the highest level of uptake and induce the highest level of transformation. These findings pertain to studies involving short exposure times in which rapid uptake is critical to induce transformation, however in chronic exposures scenarios where soluble forms, such as NiCl 2 , are maintained in the culture for two months, cellular transformation can and does occur (Pan et al, 2011). While sparingly soluble nickel compounds demonstrate a unique ability to transform cells rapidly, soluble and sparingly soluble forms are both capable of transformation and this commonality points to the shared mechanisms of toxicity for nickel compounds.…”

“…In vitro cell transformation assays demonstrate that both soluble and sparingly water soluble particulate Ni compounds are toxic to cells and interfere with long-term viability (Dipaolo and Casto, 1979; Costa et al , 1981b; Miura et al , 1989; Patierno et al , 1993; Pan et al,, 2011). However, the persistence of soluble Ni in a cell culture is an artifical situation, which is not natively replicated in vivo because soluble forms are rapidly cleared from tissues.…”

“…Here transformation was associated with alterations in signaling that support apoptosis resistance, including the activation of serine-threonine kinase Akt (Akt), the subsequent inhibition of glycogen synthase kinase 3β (GSK3β), the upregulation of the anti-apoptotic proteins, Bcl-2 and Bcl-xL, and the decreased production of ROS (Pan et al, 2011). Further research in this area is required to fully understand the mechanisms of long-term transformation by nickel, but the induction of apoptosis resistance via activation of Akt is likely an important component as Akt activation is found in many cancers and apoptosis resistance would promote the proliferation of cells with aberrant epigenetic profiles, a common feature of nickel treatment.…”

Anti-apoptotic proteins and catalase-dependent apoptosis resistance in nickel chloride-transformed human lung epithelial cells

“…These include production of reactive oxygen species (ROS), induction of DNA damage (1,4), alteration of epigenetic changes such as histone modifications (5,6), disruption of cellular iron homeostasis (7), and activation of oncogenic pathways (8,9). Despite intensive investigation, the molecular features of nickel-induced oncogenic transformation, which are essential components in tumor initiation and progression, remain elusive.…”

“…Their overexpression confers the cancer cells a growth advantage to escape from physiological surveillance and promote tumor formation (10,11). Recent studies also suggest that activation of oncogenic pathways mediate nickel chloride (NiCl 2 )-induced epithelial cell oncogenic transformation accompanied by enhanced Bcl-2, Bcl-xL protein expression (9). …”