Atf1 is a target of the mitogen-activated protein kinase Pmk1 and regulates cell integrity in fission yeast

In fission yeast, knockout of the calcineurin gene resulted in hypersensitivity to Cl(-), and the overexpression of pmp1(+) encoding a dual-specificity phosphatase for Pmk1 mitogen-activated protein kinase (MAPK) or the knockout of the components of the Pmk1 pathway complemented the Cl(-) hypersensitivity of calcineurin deletion. Here, we showed that the overexpression of ptc1(+) and ptc3(+), both encoding type 2C protein phosphatase (PP2C), previously known to inactivate the Wis1-Spc1-Atf1 stress-activated MAPK signaling pathway, suppressed the Cl(-) hypersensitivity of calcineurin deletion. We also demonstrated that the mRNA levels of these two PP2Cs and pyp2(+), another negative regulator of Spc1, are dependent on Pmk1. Notably, the deletion of Atf1, but not that of Spc1, displayed hypersensitivity to the cell wall-damaging agents and also suppressed the Cl(-) hypersensitivity of calcineurin deletion, both of which are characteristic phenotypes shared by the mutation of the components of the Pmk1 MAPK pathway. Moreover, micafungin treatment induced Pmk1 hyperactivation that resulted in Atf1 hyperphosphorylation. Together, our results suggest that PP2C is involved in a negative feedback loop of the Pmk1 signaling, and results also demonstrate that Atf1 is a key component of the cell integrity signaling downstream of Pmk1 MAPK.     

Directional Bleb Formation in Spherical Cells under Temperature Gradient

Living cells sense absolute temperature and temporal changes in temperature using biological thermosensors such as ion channels. Here, we reveal, to our knowledge, a novel mechanism of sensing spatial temperature gradients within single cells. Spherical mitotic cells form directional membrane extensions (polar blebs) under sharp temperature gradients (≥∼0.065°C μm⁻¹; 1.3°C temperature difference within a cell), which are created by local heating with a focused 1455-nm laser beam under an optical microscope. On the other hand, multiple nondirectional blebs are formed under gradual temperature gradients or uniform heating. During heating, the distribution of actomyosin complexes becomes inhomogeneous due to a break in the symmetry of its contractile force, highlighting the role of the actomyosin complex as a sensor of local temperature gradients.     

Submillisecond rotational dynamics of spin-labeled myosin heads in myofibrils.

The rotational motion of crossbridges, formed when myosin heads bind to actin, is an essential element of most molecular models of muscle contraction. To obtain direct information about this molecular motion, we have performed saturation transfer EPR experiments in which spin labels were selectively and rigidly attached to myosin heads in purified myosin and in glycerinated myofibrils. In synthetic myosin filaments, in the absence of actin, the spectra indicated rapid rotational motion of heads characterized by an effective correlation time of 10 microseconds. By contrast, little or no submillisecond rotational motion was observed when isolated myosin heads (subfragment-1) were attached to glass beads or to F-actin, indicating that the bond between the myosin head and actin is quite rigid on this time scale. A similar immobilization of heads was observed in spin-labeled myofibrils in rigor. Therefore, we conclude that virtually all of the myosin heads in a rigor myofibril are immobilized, apparently owing to attachment of heads to actin. Addition of ATP to myofibrils, either in the presence or absence of 0.1 mM Ca2+, produced spectra similar to those observed for myosin filaments in the absence of actin, indicating rapid submillisecond rotational motion. These results indicate that either (a) most of the myosin heads are detached at any instant in relaxed or activated myofibrils or (b) attached heads bearing the products of ATP hydrolysis rotate as rapidly as detached heads.     

Establishment and characterization of a cell line derived from a human serous surface papillary carcinoma of the ovary

A novel serous surface papillary carcinoma of the ovary (SSPC) cell line, HYKSSPC, was established successfully. Carcinoma cells were obtained from ascitic fluid of a 60-year-old Japanese woman. The population doubling time was 51.4 h. A phase contrast micrograph showed a pavement stone-like arrangement without contact inhibition. The chromosome number showed a wide distribution of aneuploidy, and the mode was in 46-47. An immunocytochemical study showed that CA125, BerER4 and cytokeratin were positive and that CEA, calretinin and thrombomodulin were negative. This cell line preserved some characters of the adenocarcinoma while growing in vitro. A chemosensitivity test revealed that HYKSSPC cells were sensitive to CDDP (cis-platinum), 5-fluorouracil, mitomycin C, paclitaxel and irinotecan. To our knowledge, HYKSSPC is the first established cell line derived from SSPC, and it may offer some useful information for investigating this disease.     

Specific Binding of [3H]Pyrilamine to Histamine H1 Receptors in Guinea Pig Brain In Vivo: Determination of Binding Parameters by a Kinetic Four-Compartment Model

The binding of [3H]pyrilamine, a selective ligand of histamine H1 receptors, to guinea pig brain in vivo was compared with its binding to a brain homogenate. The pharmacological properties (regional distribution, saturability, and stereoselectivity) of the [3H]pyrilamine binding in vivo were similar to those of the in vitro binding to brain homogenate. A dynamic four-compartment model was proposed for the analysis of the kinetics of [3H]pyrilamine binding in vivo. The receptor constants in vivo were determined by a computer-fitting method after correcting the radioactivity of arterial plasma and brain for the presence of radioactive metabolites. The in vivo association and dissociation were 213 and 42 times, respectively, slower than those of in vitro binding at 37 degrees C. A possible mechanism for slow association and dissociation in vivo is discussed.     

Microscopic analysis of the elastic properties of nebulin in skeletal myofibrils.

The elastic properties of nebulin were studied by measuring the elasticity of single skeletal myofibrils, from which the portion of the thin filament located at the I band had been selectively removed by treatment with plasma gelsolin under rigor conditions. In this myofibril model, a portion of each nebulin molecule at the I band was expected to be free of actin filaments and exposed. The length of the exposed portion of the nebulin molecule was controlled by performing the gelsolin treatment at various sarcomere lengths. The relation between the passive tension and extension of the exposed portion of the nebulin showed a convex curve starting from a slack length, apparently in a fashion similar to that of wool. The slack sarcomere length shifted depending on the length of the exposed portion of the nebulin, however, the relation being represented by a single master curve. The elastic modulus of nebulin was estimated to be two to three orders of magnitude smaller than that of an actin filament. Based on these results, we conclude that nebulin attaches to an actin filament in a side-by-side fashion and that it does not significantly contribute to the elastic modulus of thin filaments. The relation between the passive tension and extension of connectin (titin) was obtained for a myofibril from which thin filaments had been completely removed with gelsolin under contracting conditions; this showed a concave curve, consistent with the previous results obtained in single fibers.     

Establishment and characterization of a human malignant fibrous histiocytoma line serially transplanted in nude mice

Serial heterotransplantation of human malignant fibrous histiocytoma (MFH) derived from tibia was attempted in BALB/c nu/nu mice, and HKMFH-nu transplantable tumor line was established. This line had the following biological properties. (1) Eighteen serial passages were carried out in 41 months. (2) Morphological changes of the grafts occurred in nude mice with serial passages: During the first 6 passages, histiological picture was consistent with the common type of MFH similar to that of the original tumor, then after the 7th passage, the myxoid type coexisted with the common type, and finally the myxoid type occupied the entire grafts to form large cysts. (3) The common type grafts grew more rapidly than the myxoid type grafts. (4) Granulocytosis (neutrophilia) was observed in mice bearing the common type tumor, but not in mice bearing the myxoid type tumor.     

Differences between cell lines of uterine cervical glassy cell carcinoma and large cell nonkeratinizing squamous cell carcinoma.

Cell lines were established from two uterine cervical cancers, a glassy cell carcinoma (GCC) and a large cell nonkeratinizing squamous cell carcinoma (LCSC), and studied by a variety of techniques, including histology, chromosome analysis, heterotransplantation and tumor marker analyses. There were radical differences in the morphology, heterotransplantability, production of tumor markers, etc., between the cultures of these morphologically similar cancers. The LCSC line (HKMUS) consisted of polygonal and round cells containing tonofilaments; these cells discharged tumor antigen-4 (TA-4) into the conditioned media. HKMUS was heterotransplantable into the subcutis of nude mice to form LCSC. On the other hand, the GCC line (HOKUG) consisted of round or spindle-shaped cells. HOKUG was easily transplanted into the subcutis or intraabdominal cavity of nude mice and metastasized easily. It discharged TA-4, carbohydrate antigen 125 (CA125) and neuron-specific enolase (NSE) into the conditioned media. The histologic picture of GCC revealed numerous blood vessels and a rapid proliferation of the cells. GCC, which is considered to be a mixed carcinoma having the characteristics of both squamous carcinoma and adenocarcinoma, seems to be a cancer of unpredictable prognosis as compared to LCSC, possibly due to its rapid proliferation and easy metastasis, leading to peritonitis carcinomatosa.