A local view of cancer

Vitamin D3 suppresses morphological evolution of the cribriform cancerous phenotype

Development of cribriform morphology (CM) heralds malignant change in human colon but lack of mechanistic understanding hampers preventive therapy. This study investigated CM pathobiology in three-dimensional (3D) Caco-2 culture models of colorectal glandular architecture, assessed translational relevance and tested effects of 1,25(OH)2D3,theactive form of vitamin D. CM evolution was driven by oncogenic perturbation of the apical polarity (AP) complex comprising PTEN, CDC42 and PRKCZ (phosphatase and tensin homolog, cell division cycle 42 and protein kinase C zeta). Suppression of AP genes initiated a spatiotemporal cascade of mitotic spindle misorientation, apical membrane misalignment and aberrant epithelial configuration. Collectively, these events promoted "Swiss cheese-like" cribriform morphology (CM) comprising multiple abnormal "back to back" lumens surrounded by atypical stratified epithelium, in 3D colorectal gland models. Intestinal cancer driven purely by PTEN-deficiency in transgenic mice developed CM and in human CRC, CM associated with PTEN and PRKCZ readouts. Treatment of PTEN-deficient 3D cultures with 1,25(OH)2D3 upregulated PTEN, rapidly activated CDC42 and PRKCZ, corrected mitotic spindle alignment and suppressed CM development. Conversely, mutationally-activated KRAS blocked1,25(OH)2D3 rescue of glandular architecture. We conclude that 1,25(OH)2D3 upregulates AP signalling to reverse CM in a KRAS wild type (wt), clinically predictive CRC model system. Vitamin D could be developed as therapy to suppress inception or progression of a subset of colorectal tumors.

Patterns in space: coordinating adhesion and actomyosin contractility at E-cadherin junctions

Cadherin adhesion receptors are fundamental determinants of tissue organization in health and disease. Increasingly, we have come to appreciate that classical cadherins exert their biological actions through active cooperation with the contractile actin cytoskeleton. Rather than being passive resistors of detachment forces, cadherins can regulate the assembly and mechanics of the contractile apparatus itself. Moreover, coordinate spatial patterning of adhesion and contractility is emerging as a determinant of morphogenesis. Here we review recent developments in cadherins and actin cytoskeleton cooperativity, by focusing on E-cadherin adhesive patterning in the epithelia. Next, we discuss the underlying principles of cellular rearrangement during Drosophila germband extension and epithelial cell extrusion, as models of how planar and apical-lateral patterns of contractility organize tissue architecture.

A Jnk-Rho-Actin remodeling positive feedback network directs Src-driven invasion

Current models of tumor cell invasion propose that oncogenic signaling converges upon key orchestrators of cytoskeletal dynamics, including c-Jun N-terminal kinase (Jnk) and RhoGTPase family members; these signals dynamically direct Actin remodeling proteins (ARPs) to catalyze the cytoskeletal changes required for migration. Src is a key driver of tumor aggression, metastasis and patient mortality. To clarify how Src regulates Actin dynamics to promote invasive migration, we performed a genetic modifier screen in a Drosophila model of invasion. Nine genes linked to Actin dynamics were identified that mediate invasion in situ. We found that ARPs were required for many oncogenic effects of Src including Mmp1 expression and initiation of apoptosis. Surprisingly, they were also regulators of Jnk pathway activity: both Src and the small GTPase Rho1 activated Jnk in a manner dependent on ARPs during invasion. Our results suggest that ARPs are not simply downstream executors of signal transduction pathways. Rather, they participate in a positive feedback network involving canonical oncogenic signaling pathways that promote tumor invasion.