Melanocortin‐1 receptor structure and functional regulation

The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light.     

A general,fast, and sensitive micromethod for DNA determination: Application to rat and mouse liver,rat hepatoma,human leukocytes,chicken fibroblasts,and yeast cells

A fluorometric method using 3,5-diaminobenzoic acid for DNA determination in tissues, cultured cells, nucleated blood cells, and yeast cells is described. The method is general, simple, and rapid, and does not require prior DNA extraction, since tissue is directly solubilized in Triton X-100 and ammonia. The procedure is highly sensitive, and is able to measure rather accurately as little as 10 ng of DNA. It is applicable to all types of DNA structure. The DNA content determined in various tissues and cells was: 2.50 mg/g fresh rat liver, 3.32 mg/g rat diethylnitrosamine-induced hepatoma, 2.49 mg/g fresh mouse liver, 8.76 μg/10⁶ human leukocytes, 3.37 μg/10⁶ chicken fibroblasts, 2.97 μg/10⁸ haploid yeast cells, and 2.84 μg/10⁸ haploid yeast protoplasts.     

A novel method of multiple alignment of biopolymer sequences

A novel algorithm for multiple alignment of biological sequences is suggested. At the first step the DotHelix procedure is employed for construction of motifs, i.e. continuous fragments of local similarity of various “thickness” and strength, and then these motifs are concatenated into chains consistent with the order of letters in the sequences. The algorithm is implemented in the MA-Tools program of the GeneBee package. An example illustrating the effectivity of the algorithm is presented.     

Identification and characterization of two novel lymphocyte function-associated antigens, L24 and L25

We describe the function and cell distribution of two novel cell surface antigens, L24 and L25. These antigens are broadly distributed on human lymphocytes. Monoclonal antibodies specific for these molecules block lysis by Class I- and II-specific cytotoxic T lymphocytes, but do not affect any other T cell functions tested. Anti-L24 antibody immunoprecipitates a molecule composed of two disulfide-linked monomers of 140 kd each. Anti-L25 antibody immunoprecipitates three proteins of 150, 85, and 75 kd. The study of these and other function associated molecules may provide insight into mechanisms of cytotoxic T lymphocyte recognition and/or function.     

ATP stimulates inositol phosphates accumulation and calcium mobilization in a primary culture of rat aortic myocytes

The effects of extracellular ATP on phosphoinositide metabolism and intracellular Ca2+ concentration were studied in a primary culture of rat aortic myocytes. ATP increases the level of inositol phosphates, the putative second messenger for Ca2+ mobilization. No saturation of inositol phosphates accumulation is obtained (up to 10(-2) M ATP). Under the same conditions, ATP rapidly mobilizes intracellular Ca2+ in fura-2 loaded myocytes. The mobilization of intracellular Ca2+ is dose-dependent (maximal at 10(-4) M ATP), and is not affected by addition of EGTA. It is concluded that the receptors mediating the cytosolic increase of Ca2+ are of the P2-purinoceptor subtype. The physiological functions of these receptors are not presently known.     

In vivo environmental temperature and the in vitro pattern of luminal acidification in turtle bladders. Evidence for HCO3 ion reabsorption

In this study, it is shown how to transfer tared aliquots of (HCO3 + CO2)-containing luminal fluids directly into the mercury-sealed chamber of a modified Van Slyke apparatus and how to obtain direct as well as indirect manometric determinations of dissolved CO2 ([CO2]f) in each aliquot of such fluids. It is next shown that the pattern of in vitro luminal acidification in an isolated turtle bladder sac depends upon the prior in vivo ambient temperature to which the donor turtle had become adapted. Under in vivo conditions, the food intake, physical activity, and acid excretion of 32 degrees C-adapted turtles are greater than those of 21 degrees C or 26 degrees C-adapted turtles. Under in vitro conditions of incubating isolated bladder sacs (from 21, 26, and 32 degrees C turtles) in (HCO3 + CO2)-containing Ringer media at a single temperature (21 degrees C), the patterns of luminal acidification are as follows: (a) The rate of depletion of luminal [HCO3] is greatest in bladders from the 32 degrees C-adapted turtles. (b) Concomitant decreases in luminal [CO2]f, [HCO3], and pH (the 'CO2-decreasing patterns' of luminal acidification) develop in all bladders from 32 degrees C turtles, in half of those from 26 degrees C turtles, but in less than one-fifth of those from 21 degrees C-adapted turtles: and (c) a CO2-increasing pattern of luminal acidification is found in most of the bladders from 21 degrees C-adapted turtles. A postulated bicarbonate ion-reabsorbing pump is consistent with all of these patterns of luminal acidification.     

The receptor for human sex steroid binding protein (SBP) is expressed on membranes of neoplastic endometrium.

Sex steroid binding protein (SBP) receptor was detected on cell membranes obtained from human endometrium adenocarcinoma. The binding of SBP was proved to be highly specific, saturable, and at high affinity. It was, additionally, shown to occur at two sites at different affinities, as previously described for other human tissues. SBP was, therefore, demonstrated to recognized a specific receptor on endometrium adenocarcinoma membranes. The effect of steroid hormones on SBP-receptor interaction was also evaluated. Both dihydrotestosterone and estradiol were shown to inhibit the binding of SBP to its specific receptor on neoplastic membranes. Testosterone at a dose of 10(-9) M was shown not to interfere to a significant extent with SBP-receptor binding. The sensitivity for estradiol we had previously observed in normal premenopausal endometrium was completely lost in postmenopausal neoplastic tissue. These observations suggest that the SBP-membrane recognition system is still present in neoplastic postmenopausal endometrium, but it has been modified either by the postmenopausal endogenous milieu or by the neoplastic transformation.