Abstract
In this study, we set out to identify regulators of intact amyloid-β40/42 (Aβ) levels in A549 (p53 wild-type) and H1299 (p53-null) lung cancer cell media. Higher Aβ levels were detected in the media of A549 than H1299 cells without or with treatment with 4-methylumbelliferone (4-MU) and/or the anti-CD44 antibody (5F12). Using inhibitors, we found that PI3K, AKT, and NFκB are likely involved in regulating Aβ levels in the media. However, increased Aβ levels that more closely resembled those found upon 4-MU co-treatment resulted from MMP2/9 inhibition, suggesting that MMP2/9 maybe the main contributors to regulation of Aβ levels in the media. Differences in Aβ levels might be accounted for, in part, by p53 since blocking p53 function in A549 cells resulted in decreased Aβ levels, increased MMP2/9 levels, increased PI3K/AKT activities and the phospho/total NFκB ratio. Using siRNA targeted against MMP2 or MMP9, we found increased Aβ levels in the media, however, MMP2 knockdown led to Aβ levels closely mimicking those detected by co-treatment with 4-MU. Cell viability or apoptosis upon treatment with either MMP2 or MMP9 siRNA along with Aβ immunodepletion, showed that MMP2 is the predominant regulator of the cytotoxic effects induced by Aβ in lung cancer cells.
Highlights
Despite extensive research, lung cancer has a poor prognosis for patients with metastatic disease and remains the leading cause of cancer-related deaths with an approximate 15% 5-year survival rate in the United States and worldwide[1,2]
We subsequently showed that blocking Hyaluronic acid (HA)-CD44 signaling by IGFBP-3 resulted in increased levels of acetylcholinesterase in A549 cell media but not in the media of H1299 (p53-null) lung cancer cells, effects that correlated with a greater reduction in A549 cell viability[51]
We found that the relative abundance of Aβ oligomer versus total Aβ increased upon immunodepletion of the cytoprotective peptide, humanin, from the conditioned media of A549 and H1299 cells, leading to increased apoptosis and diminished cell viability[52]
Summary
Lung cancer has a poor prognosis for patients with metastatic disease and remains the leading cause of cancer-related deaths with an approximate 15% 5-year survival rate in the United States and worldwide[1,2]. Each of the three HAS synthesizes different molecular weights of HA and silencing HAS genes in tumors is known to block cell proliferation and metastasis[17,30] Both high levels of CD44 and HA are emerging as important metastatic markers in a wide range of human carcinomas[17,18,20,22,23,24,26,26]. The PI3K/AKT signaling pathway, known to be dysregulated in a number of human cancers, results in phosphorylation of numerous protein targets and regulates a wide range of cellular processes critical for tumorigenesis including proliferation, survival, and g rowth[35,37]. Aβ was shown to inhibit the PI3K pathway in neuronal cells inducing neurotoxicity, while activation of the PI3K pathway using a direct PI3K activator, resulted in neuroprotective effects in Aβ-induced neuronal cell death[40]
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