Proteasomes are essential for numerous cellular processes, including the cell cycle, regulation of gene expression and responses to cellular stress. Proteasome inhibitors are promising anticancer agents. The proteasome inhibitor bortezomib effectively suppresses certain types of cancer, including multiple myeloma and mantle cell lymphoma. However, bortezomib poorly inhibits solid tumors, including hepatocellular carcinoma. The activation of Akt represents an adaptive response that prevents bortezomib-induced cell apoptosis. In the present study, bortezomib induced phosphorylation of EGFR, Src and Akt in hepatoma cells and inhibition of Src reduced bortezomib-induced EGFR and Akt phosphorylation. Treatment of hepatoma cells with bortezomib led to an increase in the levels of intracellular reactive oxygen species (ROS). The ROS scavenger N-acetyl-L-cysteine inhibits bortezomib-induced ROS production and abrogates the phosphorylation of Src, epidermal growth factor receptor and Akt. The combination of bortezomib and saracatinib, a Src inhibitor, synergistically induced hepatoma cell apoptosis. The present study concluded that ROS mediated the activation of the Src-EGFR-Akt cascade by bortezomib. The combination of the Src inhibitor and bortezomib holds promise in the treatment of hepatocellular carcinoma.

AflatoxinB1 (AFB1) is well known as a potent carcinogen. Epidemiological studies have shown an association between AFB1 exposure and lung cancer in humans. AFB1 can induce the mutations of genes such as tumor suppressor p53 through its metabolite AFB1-8,9-exo-epoxide, which acts as a mutagen to react with DNA. In addition, recent study demonstrates AFB1 positively regulates type I insulin-like growth factor receptor (IGF-IR) signaling in hepatoma cells. The current study aims to determine the effects of AFB1 on Src kinase and insulin receptor substrate (IRS) in lung cancer cells and the effects of AFB1 on lung cancer cell migration. To this end, the effects of AFB1 on IRS expression, Src, Akt, and ERK phosphorylation were measured by Western blot analysis. The migration of lung cancer cells was detected by wound-healing assay. AFB1 downregulates IRS1 but paradoxically upregulates IRS2 through positive regulation of the stability of IRS2 and the proteasomal degradation of IRS1 in lung cancer cell lines A549 and SPCA-1. In addition, AFB1 induces Src, Akt, and ERK1/2 phosphorylation. Treatment of lung cancer cells with Src inhibitor saracatinib abrogates AFB1-induced IRS2 accumulation. Moreover, AFB1 stimulates lung cancer cell migration, which can be inhibited by saracatinib. We conclude that AFB1 may upregulate IRS2 and stimulate lung cancer cell migration through Src.

c-Jun N-terminal kinases (JNK) are members of the mitogen-activated protein kinase (MAPK) family that have important roles in signal transduction. The small molecule SP600125 is widely used in biochemical studies as a JNK inhibitor. However, recent studies indicate that SP600125 may also act independent of JNK. Here, we report that SP600125 can induce Src, type I insulin-like growth factor receptor (IGF-IR), Akt and Erk1/2 phosphorylation. Notably, these effects are independent of its inhibition of JNK. Inhibition of Src abrogates the stimulation of IGF-IR, Akt and Erk1/2 phosphorylation. IGF-IR knockdown blunts the induction of both Akt and Erk1/2 phosphorylation by SP600125. Moreover, combination of SP600125 and the Src inhibitor saracatinib synergistically inhibits cell proliferation. We conclude that SP600125 can activate Src-IGF-IR-Akt/Erk1/2 signaling pathways independent of JNK.