A spatiotemporally coordinated cascade of protein kinase C activation controls isoform-selective translocation.

In pituitary GH3B6 cells, signaling involving the protein kinase C (PKC) multigene family can self-organize into a spatiotemporally coordinated cascade of isoform activation. Indeed, thyrotropin-releasing hormone (TRH) receptor activation sequentially activated green fluorescent protein (GFP)-tagged or endogenous PKCbeta1, PKCalpha, PKCepsilon, and PKCdelta, resulting in their accumulation at the entire plasma membrane (PKCbeta and -delta) or selectively at the cell-cell contacts (PKCalpha and -epsilon). The duration of activation ranged from 20 s for PKCalpha to 20 min for PKCepsilon. PKCalpha and -epsilon selective localization was lost in the presence of Gö6976, suggesting that accumulation at cell-cell contacts is dependent on the activity of a conventional PKC. Constitutively active, dominant-negative PKCs and small interfering RNAs showed that PKCalpha localization is controlled by PKCbeta1 activity and is calcium independent, while PKCepsilon localization is dependent on PKCalpha activity. PKCdelta was independent of the cascade linking PKCbeta1, -alpha, and -epsilon. Furthermore, PKCalpha, but not PKCepsilon, is involved in the TRH-induced beta-catenin relocation at cell-cell contacts, suggesting that PKCepsilon is not the unique functional effector of the cascade. Thus, TRH receptor activation results in PKCbeta1 activation, which in turn initiates a calcium-independent but PKCbeta1 activity-dependent sequential translocation of PKCalpha and -epsilon. These results challenge the current understanding of PKC signaling and raise the question of a functional dependence between isoforms.

Site-directed perturbation of protein kinase C- integrin interaction blocks carcinoma cell chemotaxis.

Polarized cell movement is an essential requisite for cancer metastasis; thus, interference with the tumor cell motility machinery would significantly modify its metastatic behavior. Protein kinase C alpha (PKC alpha) has been implicated in the promotion of a migratory cell phenotype. We report that the phorbol ester-induced cell polarization and directional motility in breast carcinoma cells is determined by a 12-amino-acid motif (amino acids 313 to 325) within the PKC alpha V3 hinge domain. This motif is also required for a direct association between PKC alpha and beta 1 integrin. Efficient binding of beta 1 integrin to PKC alpha requires the presence of both NPXY motifs (Cyto-2 and Cyto-3) in the integrin distal cytoplasmic domains. A cell-permeant inhibitor based on the PKC-binding sequence of beta 1 integrin was shown to block both PKC alpha-driven and epidermal growth factor (EGF)-induced chemotaxis. When introduced as a minigene by retroviral transduction into human breast carcinoma cells, this inhibitor caused a striking reduction in chemotaxis towards an EGF gradient. Taken together, these findings identify a direct link between PKC alpha and beta 1 integrin that is critical for directed tumor cell migration. Importantly, our findings outline a new concept as to how carcinoma cell chemotaxis is enhanced and provide a conceptual basis for interfering with tumor cell dissemination.

Applying ecological and evolutionary theory to cancer: a long and winding road.

Since the mid 1970s, cancer has been described as a process of Darwinian evolution, with somatic cellular selection and evolution being the fundamental processes leading to malignancy and its many manifestations (neoangiogenesis, evasion of the immune system, metastasis, and resistance to therapies). Historically, little attention has been placed on applications of evolutionary biology to understanding and controlling neoplastic progression and to prevent therapeutic failures. This is now beginning to change, and there is a growing international interest in the interface between cancer and evolutionary biology. The objective of this introduction is first to describe the basic ideas and concepts linking evolutionary biology to cancer. We then present four major fronts where the evolutionary perspective is most developed, namely laboratory and clinical models, mathematical models, databases, and techniques and assays. Finally, we discuss several of the most promising challenges and future prospects in this interdisciplinary research direction in the war against cancer.

A disrupted expression in cancers: multiple potential causes.

Tumor cells exhibit significant variations in the rate of pro- or anti-tumoral proteins that provide them a selective advantage of growth over normal cells. The control of these rates occurs at the three DNA, RNA and protein levels, and is determined by the structure of each of these three actors for the implementation of the molecular mechanisms involved in the control of the synthesis, maturation and stability of the mRNA and the protein itself. We give here an overview of the main events that can lead to a disruption of these mechanisms.

A new mechanism of SOX9 action to regulate PKCalpha expression in the intestine epithelium.

Variations of protein kinase C (PKC) expression greatly influence the proliferation-to-differentiation transition (PDT) of intestinal epithelial cells and might have an important impact on intestinal tumorigenesis. We demonstrate here that the expression of PKCalpha in proliferating intestinal epithelial cells is repressed both in vitro and in vivo by the SOX9 transcription factor. This repression does not require DNA binding of the SOX9 high-mobility group (HMG) domain but is mediated through a new mechanism of SOX9 action requiring the central and highly conserved region of SOXE members. Because SOX9 expression is itself upregulated by Wnt-APC signaling in intestinal epithelial cells, the present study points out this transcription factor as a molecular link between the Wnt-APC pathway and PKCalpha. These results provide a potential explanation for the decrease of PKCalpha expression in colorectal cancers with constitutive activation of the Wnt-APC pathway.

Targeting of PKCalpha and epsilon in the pituitary: a highly regulated mechanism involving a GD(E)E motif of the V3 region.

Protein kinase C (PKC) has been implicated in the control of intercellular adhesion. Our previous observation demonstrating that activated PKC alpha (PKCalpha is selectively targeted to cell-cell contacts of pituitary GH3B6 cells supports these findings. The relevance of this observation is further strengthened by the present data establishing that this targeting selectivity also occurs in the pituitary gland. Moreover, a new mechanism involved in the control of PKC targeting is unravelled. We demonstrate that a three amino acid motif located in the V3 region of alpha and epsilon (epsilon (GDE/GEE respectively) is essential for the targeting selectivity of these isoforms because: (1) this motif is absent in delta (delta) and mutated in the natural D294GPKCalpha mutant, which do not exhibit such selectivity, and (2) a GEE to GGE mutation abolishes the selectivity of targeting to cell-cell contacts for epsilon, as it does for the D294G PKCalpha mutant. Thus the GD(E)E motif may be part of a consensus sequence able to interact with shuttle and/or anchoring proteins. GFP-tagged deletion mutants also reveal a new function for the pseudosubstrate in the cytoplasmic sequestration. Together, these data underline the complexity of PKC subcellular targeting in the pituitary, determined by the cell-cell contact, at least for alpha and epsilon