Keith E. Robison

Functional and structural diversity of the human Dickkopf gene family.

Wnt proteins influence many aspects of embryonic development, and their activity is regulated by several secreted antagonists, including the Xenopus Dickkopf-1 (xDkk-1) protein. xDkk-1 inhibits Wnt activities in Xenopus embryos and may play a role in induction of head structures. Here, we characterize a family of human Dkk-related genes composed of Dkk-1, Dkk-2, Dkk-3, and Dkk-4, together with a unique Dkk-3 related protein termed Soggy (Sgy). hDkks 1-4 contain two distinct cysteine-rich domains in which the positions of 10 cysteine residues are highly conserved between family members. Sgy is a novel secreted protein related to Dkk-3 but which lacks the cysteine-rich domains. Members of the Dkk-related family display unique patterns of mRNA expression in human and mouse tissues, and are secreted when expressed in 293T cells. Furthermore, secreted hDkk-2 and hDkk-4 undergo proteolytic processing which results in cleavage of the second cysteine-rich domain from the full-length protein. Members of the human Dkk-related family differ not only in their structures and expression patterns, but also in their abilities to inhibit Wnt signaling. hDkk-1 and hDkk-4, but not hDkk-2, hDkk-3 or Sgy, suppress Wnt-induced secondary axis induction in Xenopus embryos. hDkk-1 and hDkk-4 do not block axis induction triggered either by Xenopus Dishevelled (Xdsh) or Xenopus Frizzled-8 (Xfz8), both of which function to transduce signals from Wnt ligands. Thus, hDkks 1 and 4 may inhibit Wnt activity by a mechanism upstream of Frizzled. Our findings highlight the structural and functional heterogeneity of human Dkk-related proteins.

Human CARD4 Protein Is a Novel CED-4/Apaf-1 Cell Death Family Member That Activates NF-κB

The nematode CED-4 protein and its human homolog Apaf-1 play a central role in apoptosis by functioning as direct activators of death-inducing caspases. A novel human CED-4/Apaf-1 family member called CARD4 was identified that has a domain structure strikingly similar to the cytoplasmic, receptor-like proteins that mediate disease resistance in plants. CARD4 interacted with the serine-threonine kinase RICK and potently induced NF-κB activity through TRAF-6 and NIK signaling molecules. In addition, coexpression of CARD4 augmented caspase-9-induced apoptosis. Thus, CARD4 coordinates downstream NF-κB and apoptotic signaling pathways and may be a component of the host innate immune response.

Edge‐count probabilities for the identification of local protein communities and their organization

We present a computational approach based on a local search strategy that discovers sets of proteins that preferentially interact with each other. Such sets are referred to as protein communities and are likely to represent functional modules. Preferential interaction between module members is quantified via an analytical framework based on a network null model known as the random graph with given expected degrees. Based on this framework, the concept of local protein community is generalized to that of community of communities. Protein communities and higher‐level structures are extracted from two yeast protein interaction data sets and a network of published interactions between human proteins. The high level structures obtained with the human network correspond to broad biological concepts such as signal transduction, regulation of gene expression, and intercellular communication. Many of the obtained human communities are enriched, in a statistically significant way, for proteins having no clear orthologs in lower organisms. This indicates that the extracted modules are quite coherent in terms of function. Proteins 2006.