Anti-PTK2 monoclonal antibody, clone FQ952Z

A novel perichromosomal protein, which we have named chmadrin, was identified from rat kangaroo PtK2 cells. The deduced amino acid sequence revealed structural homologies in several limited regions to the Ki-67 antigen (pKi-67), The subcellular localization of chmadrin was found to be similar to that of pKi-67 throughout the cell cycle, that is, predominantly nucleolar during interphase and perichromosomal in the mitotic phase. In addition, a certain population of the protein was found to be localized in heterochromatic foci in interphase nuclei. Transient expression analysis of the truncated proteins corresponding to the conserved regions clearly demonstrated the structural basis for the characteristic cellular localization. Residues 494-778, which show extensive similarity to the corresponding region of pKi-67, were efficiently targeted to nucleoli, whereas a repetitive structure found at the C-terminal portion, whose similarity to pKi-67 is weak, was localized precisely to mitotic chromosomes. The C-terminal portion was designated the 'LR domain" since several LR (leucine and arginine) pairs commonly appear in chmadrin and pKi-67, When overproduced in the interphase nuclei, the LR domain induced the formation of aberrant heterochromatin as a structural constituent. These are the first empirical data suggesting the involvement of perichromosomal proteins in the organization of chromatin structure.

Materials of defined elasticity, including synthetic material scaffolds and tissue-derived matrices, can regulate biological responses of cells and in particular adhesion, migration, growth and differentiation which are essential parameters for tissue integration. These responses have been extensively investigated in interphase cells, but little is known whether and how material elasticity affects mitotic cells. We used polyelectrolyte multilayer films as model substrates with elastic modulus ranging from Eap = 0 up to Lap = 500 kPa and mitotic PtK2 epithelial cells to address these important questions. Soft substrates (Eap < 50 kPa) led to abnormal morphology in chromosome segregation, materialized by chromatin bridges and chromosome lagging. Frequency of these damages increased with decreasing substrate stiffness and was correlated with a pro-apoptotic phenotype. Mitotic spindle was not observed on soft substrates where formation of chromatin damages is due to low beta 1-integrin engagement and decrease of Rac1 activities. This work constitutes the first evidence that soft substrates hinder epithelial cell division. In perspective, our findings emphasize the prime incidence of the material elasticity on the fate of the phenotype, especially of stem cells in the mitotic phase. (C) 2011 Elsevier Ltd. All rights reserved.