Isolation of the intercellular glycoproteins of desmosomes.

183

Abstract. Desmosomal glycoproteins 2 and 3 (dg2 and 3) or desmocollins have been implicated in desmosome adhesion. We have obtained a 5.0-kb-long clone for dg3 from a bovine nasal epidermal hgtl 1 cDNA library. Sequence analysis of this clone reveals an open reading frame of 2,517 bases encoding a polypeptide of 839 amino acids. The sequence consists of a signal peptide of 28 amino acids, a precursor sequence of 104 amino acids, and a mature protein of 707 amino acids. The latter has the characteristics of a transmembrane glycoprotein with an extracellular domain of 550 amino acids and a cytoplasmic domain of 122 amino acids.The sequence of a partial clone from the same library shows that dg2 has an alternative COOH terminus that is extended by 54 amino acids. Genomic DNA sequence data show that this arises by splicing out of a 46-bp exon that encodes the COOH-terminal 11 amino acids of dg3 and contains an in-frame stop codon.The extraceUular domain of dg3 shows 39.4% protein sequence identity with bovine N-cadherin and 28.4% identity with the other major desmosomal glycoprotein, dgl, or desmoglein. The cytoplasmic domain of dg3 and the partial cytoplasmic domain of rig2 show 23 and 24% identity with bovine N-cadherin, respectively.The results support our previous model for the transmembrane organization of dg2 and

Section: Discussionsupporting

confidence: 56%

Cloning and sequence analysis of desmosomal glycoproteins 2 and 3 (desmocollins): cadherin-like desmosomal adhesion molecules with heterogeneous cytoplasmic domains.

Collins

Legan

Kenny

et al. 1991

183

“…Although morphological changes in the keratin filament network have been associated with terminal differentiation, they have not been positively linked with the appearance of these large keratins. Such changes include the interaction between keratin filaments and desmosomal plaques (33)(34)(35)(36)(37)(38), and the formation of bundles (macrofibrils) of keratin filaments (39,40). Nonethless, the finding that large keratins are expressed in all vertebrate epidermis and primarily in epidermis rather than internal epithelia, suggests that…”

Section: Discussionmentioning

confidence: 99%

Expression of unusually large keratins during terminal differentiation: balance of type I and type II keratins is not disrupted.

Kim¹,

Marchuk²,

Fuchs³

1984

When a basal epidermal cell undergoes a commitment to terminally differentiate, it ceases to divide and begins to migrate outward towards the surface of the skin. Dramatic changes in its cytoskeletal architecture take place, accompanied by numerous changes in the expression of keratins, a family of related polypeptides that form 8-nm filaments in these cells. We show here that a shift to the synthesis of unusually large keratins occurs that does not seem to disrupt the ratio of two distinct subfamilies of keratins. Preliminary studies indicate that this differentiation-specific shift may be at the level of transcriptional rather than post-trancriptional regulation. The striking similarities between these large keratins and the type I and type II keratins of basal epidermal cells suggests the important role that both classes of large keratin sequences must play in the assembly of the intermediate filaments within the differentiating keratinocyte.Several laboratories have reported differences between the keratins of stratum corneum and those of the living layers of epidermis (1--4). During the course of terminal differentiation, changes occur in the expression of the keratin polypeptides that comprise the 8-nm tonofilaments (5-10). For the human, keratins of size 46, 48.5, 50, 52, 56, and 58 kd are synthesized by the basal epidermal cells (Fig. 1, lane 1), whereas additional keratins of size 67, 65.5, and 56.5 kd are produced by the terminally differentiating epidermis (lane 3). As the cells pass through the granular layer to the stratum corneum, a slight reduction in the size of the keratins takes place. As judged by in vitro translation of mRNAs isolated from basal (lane 2) and differentiating (lane 4) keratinocytes, the changes in keratin pattern that occur early in the course of terminal differentiation are clearly at the level of mRNA biosynthesis (5).Recently, it was demonstrated that the keratins produced by basal epidermal cells can be divided into two distinct groups based on the ability of their mRNAs to cross-hybridize with two different cloned keratin cDNAs (11). Other epithelia express different subsets of keratins, but most if not all of these seem to be similar to one or the other of the two epidermal keratin subfamilies (12). The small (40-52 kd) and relatively acidic keratins have been named the type I class, and the large (53-58 kd) and more basic keratins have been named the type II class (13,14). At least one member of each of the two keratin types seem to be expressed in all cells at all times, suggesting their combined importance in filament assembly (14). Sequence analyses (13,(15)(16)(17)(18) have shown that while the two types of keratins share only low (<30%) homology, their predicted secondary structures are strikingly similar and are compatible with their playing an essential role in forming the coiled-coil backbone of the protofilament of the 8-nm keratin filament (13,18).The keratins typical of terminally differentiating keratinocytes seem to be unusually large and are not fo...

“…The purification of desmosomes from fresh bovine muzzle epidermis, and the separation of membrane core glycoproteins from cytoplasmic plaque proteins were performed as described previously (15,31,36).…”

Section: Bovine Muzzle Epidermismentioning

confidence: 99%

Regulation of desmosome assembly in MDCK epithelial cells: coordination of membrane core and cytoplasmic plaque domain assembly at the plasma membrane.

Pasdar¹,

Krzeminski²,

Nelson³

1991

Abstract. Desmosomes are major components of the intercellular junctional complex in epithelia. They consist of at least eight different cytoplasmic and integral membrane proteins that are organized into two bioehemically and structurally distinct domains: the cytoplasmic plaque and membrane core. We showed previously that in MDCK epithelial cells major components of the cytoplasmic plaque (desmoplakin I and 1I; DPI/II) and membrane core domains (desmoglein I; DGI) initially enter a pool of proteins that is soluble in buffers containing Triton X-100, and then titrate into an insoluble pool before their arrival at the plasma membrane (Pasdar, M., and W. J. Nelson. 1988. J. Cell Biol. 106:677-685; Pasdar, M., and W. J. Nelson. 1989. J. Cell Biol. 109:163-177). We have now examined whether either the soluble or insoluble pool of these proteins represents an intracellular site for assembly and interactions between the domains before their assembly into desmosomes at the plasma membrane. Interactions between the Triton X-100-soluble pools of DPI/II and DGI were analyzed by sedimentation of extracted proteins in sucrose gradients. Results show distinct differences in the sedimentation profiles of these proteins, suggesting that they are not associated in the Triton X-100-soluble pool of proteins; this was also supported by the observation that DGI and DPI/II could not be coimmunoprecipitated in a complex with each other from sucrose gradient fractions. Immunofluorescence analysis of the insoluble pools of DPI/II and DGI, in cells in which desmosome assembly had been synchronized, showed distinct differences in the spatial distributions of these proteins. Furthermore, DPI/II and DGI were found to be associated with different elements of cytoskeleton; DPI/II were located along cytokeratin intermediate filaments, whereas DGI appeared to be associated with microtubules. The regulatory role of cytoskeletal elements in the intracellular organization and assembly of the cytoplasmic plaque and membrane core domains, and their integration into desmosomes on the plasma membrane is discussed.