Activating mutations in KRAS and in one of its downstream mediators, BRAF, have been identified in a variety of human cancers. To determine the role of mutations in BRAF and KRAS in ovarian carcinoma, we analyzed both genes for three common mutations (at codon 599 of BRAF and codons 12 and 13 of KRAS). Mutations in either codon 599 of BRAF or codons 12 and 13 of KRAS occurred in 15 of 22 (68%) invasive micropapillary serous carcinomas (MPSCs; low-grade tumors) and in 31 of 51 (61%) serous borderline tumors (precursor lesions to invasive MPSCs). None of the tumors contained a mutation in both BRAF and KRAS. In contrast, none of the 72 conventional aggressive high-grade serous carcinomas analyzed contained the BRAF codon 599 mutation or either of the two KRAS mutations. The apparent restriction of these BRAF and KRAS mutations to low-grade serous ovarian carcinoma and its precursors suggests that low-grade and high-grade ovarian serous carcinomas develop through independent pathways.

Conclusions: Active MAPK is more frequently expressed in low-grade than in high-grade ovarian serous carcinoma. Active MAPK serves as a good prognostic marker in patients with high-grade serous carcinomas.

The clonal relationship between ovarian high‐grade serous carcinoma (HGSC) and its presumed precursor lesion, serous tubal intraepithelial carcinoma (STIC), has been reported. However, when analyzing patients with concurrent ovarian carcinoma and tubal lesion, the extensive carcinoma tissues present at diagnosis may have effaced the natural habitat of precursor clone(s), obscuring tumor clonal evolutionary history, or may have disseminated to anatomically adjacent fimbriae ends, masquerading as precursor lesions. To circumvent these limitations, we analyzed the genomic landscape of incidental tubal precursor lesions including p53 signature, dormant STIC or serous tubal intraepithelial lesion (STIL) and proliferative STIC in women without ovarian carcinoma or any cancer diagnosis using whole‐exome sequencing and amplicon sequencing. In three of the four cancer‐free women with multiple discrete tubal lesions we observed non‐identical TP53 mutations between precursor lesions from the same individual. In one of the four women with co‐existing ovarian HGSC and tubal precursor lesion we found non‐identical TP53 mutations and a lack of common mutations shared between her precursor lesion and carcinoma. Analyzing the evolutionary history of multiple tubal lesions in the same four patients with concurrent ovarian carcinoma indicated distinct evolution trajectories. Collectively, the results support diverse clonal origins of tubal precursor lesions at the very early stages of tumorigenesis. Mathematical modeling based on lesion‐specific proliferation rates indicated that p53 signature and dormant STIC may take a prolonged time (two decades or more) to develop into STIC, whereas STIC may progress to carcinoma in a much shorter time (6 years). The above findings may have implications for future research aimed at prevention and early detection of ovarian cancer. Copyright © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Isometric tension, stiffness and the cross‐bridge kinetics in rabbit soleus slow‐twitch fibres (STFs) were studied in the temperature range 5‐37°C by sinusoidal analysis. The effects of MgATP and phosphate (Pi) on the cross‐bridge kinetics were studied, and the temperature dependence of the kinetic constants of elementary steps of the cross‐bridge cycle was deduced in the range 20‐37°C. The MgATP association constant (K1a) decreased when temperature was increased. The rate constants of the ATP‐isomerization step (k1b and k‐1b) and the cross‐bridge detachment step (k2, and k‐2) had Q10 values of 3‐4, and hence their equilibrium constants (K1b and K2) changed little with temperature. Q 10 of the force generation step (k4) was the largest at 6.7; its reversal step (k‐4) had a Q10 of 2.5, and hence its equilibrium constant (K4) increased significantly with temperature. The Pi association constant (K5) changed little with temperature. The elementary steps of the cross‐bridge cycle are more temperature sensitive in soleus STFs than in psoas, which are fast‐twitch fibres. This is in accord with a higher temperature sensitivity of the apparent rate constants in STFs. The temperature dependence of the equilibrium constant of the force generation step (K4) was fitted to the modified Van't Hoff equation to deduce standard enthalpy change (ΔH°; 70 ± 20 kJ mol−1), standard entropy change (ΔS°; 250 ± 70 J mol−1 K−1), and heat capacity change (ΔCp; −12 ± 5 kJ mol−1 K−1). These results indicate that the force generation step is an entropy driven, endothermic reaction that accompanies a burial of large surface area. These observations are consistent with the hypothesis that hydrophobic interaction between residues of actin and myosin and between residues of the myosin head underlies the mechanism of force generation. An increase of isometric tension with temperature is accounted for by the increased number of cross‐bridges in tension generating states. Stiffness also increased with temperature, but to a lesser degree.

The force-generation and phosphate-release steps of the cross-bridge cycle in rabbit soleus slow-twitch muscle fibers (STF) were investigated using sinusoidal analysis, and the results were compared with those of rabbit psoas fast-twitch fibers (FTF). Single fiber preparations were activated at pCa 4.40 and ionic strength 180 mM at 20 degrees C. The effects of inorganic phosphate (Pi) concentrations on three exponential processes, B, C, and D, were studied. Results are consistent with the following cross-bridge scheme: [formula: see text] where A is actin, M is myosin, D is MgADP, and P is inorganic phosphate. The values determined are k4 = 5.7 +/- 0.5 s-1 (rate constant of isomerization step, N = 9, mean +/- SE), k-4 = 4.5 +/- 0.5 s-1 (rate constant of reverse isomerization), K4 = 1.37 +/- 0.13 (equilibrium constant of the isomerization), and K5 = 0.18 +/- 0.01 mM-1 (Pi association constant). The isomerization step (k4) in soleus STF is 20 times slower, and its reversal (k-4) is 20 times slower than psoas fibers. Consequently, the equilibrium constant of the isomerization step (K4) is the same in these two types of fibers. The Pi association constant (K5) is slightly higher in STF than in FTF, indicating that Pi binds to cross-bridges slightly more tightly in STF than FTF. By correlating the cross-bridge distribution with isometric tension, it was confirmed that force is generated during the isomerization (step 4) of the AMDP state and before Pi release in soleus STF.