PIN1 is an E2F target gene essential for Neu/Ras-induced transformation of mammary epithelial cells

Growth factor signaling induces metastasis genes in transformed cells: molecular connection between Akt kinase and osteopontin in breast cancer

Malignant tumors are characterized by excessive growth, immortalization, and metastatic spread, whereas benign tumors do not express gene products that mediate invasion. The molecular basis for this difference is incompletely understood. We have screened signal transduction molecules associated with the epidermal growth factor (EGF) receptor and have identified constitutive phosphorylation, indicative of activation, of Akt kinase in MT2994 breast cancer cells. In contrast, cells of the benign breast epithelial cell lines Comma-D and FSK-7 are immortalized through pathways that are independent of the EGF-phosphatidylinositol 3-kinase-Akt kinase cascade, but this is not associated with invasiveness. Transfection of constitutively active Akt kinase causes accelerated cell division and osteopontin expression. Conversely, dominant-negative Akt kinase slows cell cycle progression and suppresses osteopontin expression. The manipulation of osteopontin expression in this setting by transfection of the gene or its antisense does not affect the growth rate of the cells but alters cell motility and anchorage independence. Therefore, Akt kinase activates two distinct genetic programs: the program of growth and survival, which is independent of osteopontin expression, and the program of invasiveness and anchorage independence, which is mediated by osteopontin. These studies define Akt kinase as a molecular bridge between cell cycle progression and dissemination.

Peptide binding induces large scale changes in inter-domain mobility in human Pin1

Pin1 is a peptidyl-prolyl cis/trans isomerase (PPIase) essential for cell cycle regulation. Pin1-catalyzed peptidyl-prolyl isomerization provides a key conformational switch to activate phosphorylation sites with the common phospho-Ser/Thr-Pro sequence motif. This motif is ubiquitously exploited in cellular response to a variety of signals. Pin1 is able to bind phospho-Ser/Thr-Pro-containing sequences at two different sites that compete for the same substrate. One binding site is located within the N-terminal WW domain, which is essential for protein targeting and localization. The other binding site is located in the C-terminal catalytic domain, which is structural homologous to the FK506-binding protein (FKBP) class of PPIases. A flexible linker of 12 residues connects the WW and catalytic domain. To characterize the structure and dynamics of full-length Pin1 in solution, high resolution NMR methods have been used to map the nature of interactions between the two domains of Pin1. In addition, the influence of target peptides on domain interactions has been investigated. The studies reveal a dynamic picture of the domain interactions. 15N spin relaxation data, differential chemical shift mapping, and residual dipolar coupling data indicate that Pin1 can either behave as two independent domains connected by the flexible linker or as a single intact domain with some amount of hinge bending motion depending on the sequence of the bound peptide. The functional importance of the modulation of relative domain flexibility in light of the multitude of interaction partners of Pin1 is discussed.

Prolyl isomerase Pin1: a catalyst for oncogenesis and a potential therapeutic target in cancer

Phosphorylation of proteins on serine or threonine residues preceding proline (Ser/Thr-Pro) is a major intracellular signaling mechanism. The phosphorylated Ser/Thr-Pro motifs in a certain subset of phosphoproteins are isomerized specifically by the peptidyl-prolyl cis-trans isomerase Pin1. This post-phosphorylation isomerization can lead to conformational changes in the substrate proteins and modulate their functions. Pin1 interacts with a number of mitotic phosphoproteins, and plays a critical role in mitotic regulation. Recent work indicates that Pin1 is overexpressed in many human cancers and plays an important role in oncogenesis. Pin1 regulates the expression of cyclin D1 by cooperating with Ras signaling and inhibiting the interaction of beta-catenin with the tumor suppressor APC and also directly stabilizing cyclin D1 protein. Furthermore, PIN1 is an E2F target gene essential for the Neu/Ras-induced transformation of mammary epithelial cells. Pin1 is also a critical regulator of the tumor suppressor p53 during DNA damage response. Given its role in cell growth control and oncogenesis, Pin1 could represent a new anti-cancer target.

The prolyl isomerase Pin1 in breast development and cancer

The prolyl isomerase Pin1 specifically isomerizes certain phosphorylated Ser/Thr-Pro bonds and thereby regulates various cellular processes. Pin1 is a target of several oncogenic pathways and is overexpressed in human breast cancer. Its overexpression can lead to upregulation of cyclin D1 and transformation of breast epithelial cells in collaboration with the oncogenic pathways. In contrast, inhibition of Pin1 can suppress the transformation of breast epithelial cells. In addition, Pin1 knockout in mice prevents massive proliferation of breast epithelial cells during pregnancy. Pin1 plays a pivotal role in breast development and may be a promising new anticancer target.