Plectin-Isoform-Specific Rescue of Hemidesmosomal Defects in Plectin (–/–) Keratinocytes

Abstract

The various plectin isoforms are among the major crosslinking elements of the cytoskeleton. The importance of plectin in epithelia is convincingly supported by the severe skin blistering observed in plectin-deficient humans and mice. Here, we identified plectin 1a (> 500 kDa), a full length plectin variant containing the sequence encoded by the alternative first exon 1a, as the isoform most prominently expressed in human and mouse keratinocytes. In skin sections and cultured keratinocytes, plectin 1a was shown to colocalize with hemidesmosomal structures. In contrast, a second isoform expressed in epithelia, plectin 1c, differing from 1a merely by a short N-terminal sequence, colocalized with microtubules. Expression of plectin 1a, but not of its N-terminal fragment alone, or of a third alternative full length isoform (plectin 1), restored the reduced number of hemidesmosome-like stable anchoring contacts in cultured plectin-null keratinocytes. Our results show for the first time that different isoforms of a cytolinker protein expressed in one cell type perform distinct functions. Moreover, the identification of plectin 1a as the isoform defects in which cause skin blistering in plectin-related genetic diseases, such as epidermolysis bullosa simplex MD and epidermolysis bullosa simplex Ogna, could have implications for the future development of clinical therapies for patients.

Bpag1 localization to actin filaments and to the nucleus is regulated by its N-terminus

“…Furthermore, fusion protein analysis in C2C12 cells showed that the nature of the isoform-specific unique region upstream from the ABD has a major impact both on the way the ABD interacts with the actin cytoskeleton and with the role of the plakin domain region in localizing the protein to the nucleus. These results, in combination with recent results with various plectin isoforms in keratinocytes (Andra et al, 2003), indicate that unique N-terminal regions are necessary for regulating the localization and function of plakin proteins.…”

“…The N-terminal unique regions in plectin were hypothesized to optimize its function in a cell-dependent manner. The possibility of differential subcellular localization and function of plectin isoforms containing different N-terminal sequences has recently been addressed within a single cell type, keratinocytes (Andra et al, 2003). It was shown that alternate N-terminal sequences could determine the localization of plectin isoforms to either hemidesmosomes or to microtubules.…”

Unexpected gain of function for the scaffolding protein plectin due to mislocalization in pancreatic cancer

“…Our results indicate that plectin-1a overexpression can induce HPDE cells to produce more exosomes, but plectin-1a alone is not sufficient to produce exosomes to the level of cancer cells, because no exosomes were detectable in the case of keratinocytes that express high levels of plectin-1a ( Fig. 2A) (21).…”

“…In assessing whether normal cells that produce abundant exosomes (JAWSII immature dendritic cells) (20) or cells that are rich in cytosolic plectin (keratinocyte, melanocyte, and C6 glioma) (21,22) also have plectin on their cell surface (Fig. S1D), we found that, unlike PDAC cells, these types of cells did not exhibit PTP surface binding.…”

“…The plectin locus has a complex organization, with 11 alternative first exons, 8 of which are coding, giving rise to at least eight different plectin isoforms (24). Based on the distinct roles played by different plectin isoforms in normal cells, the cytoplasmic expression of plectin in normal keratinocytes (21,24,25), and our previous findings of plectin overexpression and cell surface localization in PDAC (7), we sought to investigate the profile of plectin isoforms in PDAC cell lines. We found that HPDE cells and PDAC cell lines express comparable levels of total plectin (Fig.…”