instruction:
In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.
question:
Context: Most melanomas harbor oncogenic BRAF(V600) mutations, which constitutively activate the MAPK pathway. Although MAPK pathway inhibitors show clinical benefit in BRAF(V600)-mutant melanoma, it remains incompletely understood why 10% to 20% of patients fail to respond. Here, we show that RAF inhibitor-sensitive and inhibitor-resistant BRAF(V600)-mutant melanomas display distinct transcriptional profiles. Whereas most drug-sensitive cell lines and patient biopsies showed high expression and activity of the melanocytic lineage transcription factor MITF, intrinsically resistant cell lines and biopsies displayed low MITF expression but higher levels of NF-κB signaling and the receptor tyrosine kinase AXL. In vitro, these MITF-low/NF-κB-high melanomas were resistant to inhibition of RAF and MEK, singly or in combination, and ERK. Moreover, in cell lines, NF-κB activation antagonized MITF expression and induced both resistance marker genes and drug resistance. Thus, distinct cell states characterized by MITF or NF-κB activity may influence intrinsic resistance to MAPK pathway inhibitors in BRAF(V600)-mutant melanoma.\Question: Does a melanoma cell state distinction influence sensitivity to MAPK pathway inhibitors?
answer:
Although most BRAF(V600)-mutant melanomas are sensitive to RAF and/or MEK inhibitors, a subset fails to respond to such treatment. This study characterizes a transcriptional cell state distinction linked to MITF and NF-κB that may modulate intrinsic sensitivity of melanomas to MAPK pathway inhibitors.


question:
Context: Nonviral vectors based on polyethylenimine (PEI) usually contain an excess of PEI that is not complexed to DNA. Since unbound PEI contributes to cellular and systemic toxicity, purification of polyplexes from unbound PEI is desirable.', 'Size exclusion chromatography (SEC) was used to purify PEI polyplexes of free PEI. Transfection properties of purified polyplexes and the effect of free PEI on gene delivery were studied in vitro and in vivo after systemic application into mice.', 'SEC did not change the size and zeta-potential of polyplexes. Independent of the amount of PEI used for complex formation, purified PEI polyplexes had the same final PEI nitrogen/DNA phosphate ratio of 2.5. Notably, purified PEI polyplexes demonstrated low cellular and systemic toxicity. High transfection efficiency was achieved with purified polyplexes at high DNA concentrations (8-15 microg/ml). At low DNA concentrations (2-4 microg/ml) gene transfer with purified particles was less efficient than with polyplexes containing free PEI both in vitro and in vivo. Mechanistic studies showed that free PEI partly blocked cellular association of DNA complexes but was essential for the following intracellular gene delivery. Adding free PEI to cells treated with purified particles with a delay of up to 4 h resulted in significantly enhanced transfection efficiency compared with non-purified particles or purified particles without free PEI.\Question: Does purification of polyethylenimine polyplexes highlight the role of free polycations in gene transfer?
answer:
This study presents an efficient method to remove free PEI from PEI polyplexes by SEC. Our results from transfection experiments demonstrate that free PEI substantially contributes to efficient gene expression but also mediates toxic effects in a dose-dependent manner. Purified polyplexes without free PEI have to be applied at increased concentrations to achieve high transfection levels, but exhibit a greatly improved toxicity profile.


question:
Context: Calcium channel blockers (CCBs) inhibit the migration of vascular smooth muscle cells (VSMC) by mechanisms that remain poorly understood. The purpose of the present study was to characterize the signaling mechanisms by which CCBs inhibit VSMC migration.', 'Nifedipine potently inhibited platelet-derived growth factor (PDGF)-induced chemotaxis, collagen I-induced haptotaxis, and wound-induced migration of human aortic VSMC. In addition, nifedipine inhibited PDGF-induced membrane ruffling and lamellipodium formation. PDGF-induced VSMC migration was significantly inhibited by PP2, a selective inhibitor of the Src kinase family, and was also significantly inhibited by the expression of kinase-inactive Src, suggesting that Src is required for VSMC migration. Nifedipine also inhibited PDGF-induced Src activation (by 60+/-4% with 30 microM) and tyrosinephosphorylation of Cas, paxillin, and cortactin, which are actin-associated substrates of Src. RNA interference-induced knockdown of the Ca(2+)-dependent tyrosine kinase, Pyk2, resulted in inhibition of PDGF-induced Src activation and migration. Finally, nifedipine inhibited PDGF-induced Pyk2 activation in a dose-dependent manner.\Question: Does nifedipine interfere with migration of vascular smooth muscle cells via inhibition of Pyk2-Src axis?
answer:

These data suggest that nifedipine interferes with VSMC migration via inhibition of the Pyk2-Src axis and inhibition of actin remodeling processes, including membrane ruffling and lamellipodium formation.