The interaction of Phe472 with a fluorescent inhibitor bound to the complex of myosin subfragment-1 with nucleotide

Analysis of differently expressed proteins involved in metastatic niche of lung

BACKGROUND

The "seed and soil" hypothesis for metastasis was a pivotal milestone in the study of malignant disease. Recently, growing studies have focused on the tumor secretory factors that may mediate preparation of the "metastatic soil." A suitable environment for the metastatic lesions was created by many inflammatory cytokines in the lung, whichwas verified by in vivo experimental models. In 2005, a pre-metastatic niche and metastatic niche modelwere suggested by David Lyden and Bethan Psaila, to delineate the interactions between malignant cells and their microenvironment at the metastatic site, whichsoon became the most importanthypothesis. However, the evidence is limited to animal models. More clinical evidence is needed to support this hypothesis.

METHODS

Human lung specimens were taken from different regions within metastatic lung tissue and normal lung tissue. Differently expressed proteins were analyzed by using the two dimensional fluorescent difference gel electrophoresis (2-D DIGE) technology: about 0.5-1 cm (Tissue 1) of lung tissue was taken adjacent to the metastatic tumor; about 1 cm (Tissue 2) of lung tissue was taken far away from the metastatic tumor; and normal lung tissue of the inflammatory pseudotumor (Tissue 3) was taken at least 3 cm away from the pseudotumor. We usedmatrix-assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF/TOFMS) analysis to identify differently expressed proteins in T1, T2, andT3 samples.

RESULTS

T1 samples were different from T2 samples in the expression of 27 proteins. T2 samples had different expressions in 24 proteins, compared to T3 samples.Nine proteins were expressed differently between T1 and T3 samples. These proteins are mainly involved inenergy metabolism, protect the tumor cell from immunologic engraftment of metastatic tumor cells, and migration. Some of thesehave been reported to be related to the tumor metastatic niche hypothesis: Type VI collagen, heat shock protein 90, and Fibrinogen.

CONCLUSION

The type VI collagen, heat shock protein 90, and Fibrinogen were selected aspotential niche proteins. These findings support the metastatic niche hypothesis and encourage further studies.

2,4-Dinitrophenol reduces the reactivity of Lys553 in the lower 50-kDa region of myosin subfragment 1

2,4-Dinitrophenol (DNP) increases the affinity of myosin for actin and accelerates its Mg(2+)ATPase activity, suggesting that it acts on a region of the myosin head that transmits conformational changes to actin- and ATP-binding sites. The binding site/s for DNP are unknown; however similar hydrophobic compounds bind to the 50-kDa subfragment of the myosin head, near the actin-binding interface. In this region, a helix-loop-helix motif contains Lys553, which is specifically labeled with the fluorescent probe 6-[fluorescein-5(and 6)-carboxamido] hexanoic acid succinimidyl ester (FHS). This reaction is sensitive to conformational changes in the helix-loop-helix and the labeling efficiency was reduced when S1 was bound to actin, DNP or nucleotide analogs. The nucleotide analogs had a range of effects (PPi>ADP·AlF(4)(-)>ADP) irrespective of the open-closed state of switch 2. The greatest reduction in labeling was in the presence of actin or DNP. When we measured the effect of each ligand on the fluorescence of FHS previously attached to S1, only DNP quenched the emission. Together, the results suggest that the helix-loop-helix region is flexible, it is part of the communication pathway between the ATP- and actin-binding sites of myosin and it is proximal to the region of myosin where DNP binds.