Phorbol ester serves as a coepibolin in the spreading of primary guinea pig epidermal cells.

In earlier studies, it was shown that the human plasma-spreading glycoprotein, epibolin (the 65 kD species of serum-spreading factor or vitronectin), requires a second plasma component, termed coepibolin, in order to support maximal dissociated epidermal cell spreading in tissue culture. Whereas epibolin alone in defined medium supports some cell spreading, the purified plasma coepibolin preparations do not effect spreading in the absence of epibolin. Although not yet entirely purified, coepibolin associates with some plasma fractions but not with others; it is certainly not a property of all proteins, e.g., while bovine serum albumin (BSA) has coepibolin activity, ovalbumin does not. The data presented here show that the phorbol ester, 12-tetra-decanoyl-1-phorbol-13-acetate (TPA) can act as a potent coepibolin and support maximal spreading over a concentration range of 10-100 ng/ml. In the absence of epibolin TPA does not stimulate the spreading of epidermal cells when given alone or in the presence of BSA or ovalbumin. Coepibolin activity appears to associate with tumor-promoting activity in that the phorbol derivative, phorbol-12,13-didecanoate, shows coepibolin activity, while its inactive non-tumor-promoting isomer, phorbol-4 alpha-phorbol-12,13-didecanoate, does not. These data suggest that the proteinaceous plasma-derived cofactor acts in a fashion similar to TPA and that this as yet unexplained mechanism of TPA action is important to the full expression of epibolin and to the early phase of epidermal cell spreading.

Cation dependence of guinea pig epidermal cell spreading.

To understand the earliest phases of epidermal cell spreading we have sought a defined in vitro system. We studied the divalent cation dependence of guinea pig epidermal cell spreading in media containing varying concentrations of cations. No spreading occurred in calcium-magnesium-free Dulbecco's modified Eagle's medium (CMF-DME) in the presence of cation-free fetal bovine serum; however, significant spreading occurred if the medium was supplemented with Mg++ plus Ca++ or Mg++ alone. Supplementing with Ca++ alone led to much less spreading. These cations in CMF-DME did not support spreading in the absence of serum or the presence of serum albumin. Assaying cell spreading in a simple salt solution consisting of NaCl, KCl, Tris buffer, pH 7.4 plus dialyzed serum and a series of divalent cation supplements (Ca++, Mg++, Mn++, Co++, Zn++, Ni++), showed that only Mg++ and Mn++, and to a lesser extent, Ca++, supported cell spreading. In contrast to Mg++, however, Mn++ could support spreading in the absence of whole serum if serum albumin were present. Although Mn++ plus serum albumin supported more rapid spreading at lower cation concentrations than Mg++ plus serum, equal concentrations of Ca++ completely blocked the Mn++ effect. In contrast to the increasing cell spreading, which occurred in Mg++-containing medium with time, cell death occurred in Mn++-containing medium by 24 h. Consonant with studies from other laboratories, human foreskin fibroblasts spread in Mn++-containing salt solution in the absence of protein supplements. These experiments indicate for epidermal cell spreading that Mg++ is the important cation in tissue culture media, that under proper cation conditions epidermal cells do not need a specific spreading protein (i.e. a protein that has been demonstrated to support cell spreading), that Mn++ and Mg++-induced spreading seem to represent different mechanisms, that fibroblastic and epidermal cells have different cation requirements for in vitro spreading, and that the crucial role cations play in cell spreading remains to be elucidated.

Parallel computation of multiple biological sequence comparisons.

A parallel implementation of an efficient method for comparison of multiple DNA sequences is presented. The method is described in terms of a conceptual tree data structure for the sequences to be compared. The parallel algorithm shows efficient utilization of processors on an Encore Multimax computer in a sample comparison of 11 sequences totaling over 4000 bases. Timing data show the strong influence of computer system details on this parallel program. Also presented is a graphics program for displaying multiple sequence comparison output data. The display is capable of representing large volumes of multiple sequence comparison data in a single plot. The program has several additional features that allow closer examination of subsets of sequences. A display of matches from the sample comparison reflects the known structure of these sequences.

Supercomputers and biological sequence comparison algorithms.

Comparison of biological (DNA or protein) sequences provides insight into molecular structure, function, and homology and is increasingly important as the available databases become larger and more numerous. One method of increasing the speed of the calculations is to perform them in parallel. We present the results of initial investigations using two dynamic programming algorithms on the Intel iPSC hypercube and the Connection Machine as well as an inexpensive, heuristically-based algorithm on the Encore Multimax.