Architectural control of metabolic plasticity in epithelial cancer cells.

Metabolic plasticity enables cancer cells to switch between glycolysis and oxidative phosphorylation to adapt to changing conditions during cancer progression, whereas metabolic dependencies limit plasticity. To understand a role for the architectural environment in these processes we examined metabolic dependencies of cancer cells cultured in flat (2D) and organotypic (3D) environments. Here we show that cancer cells in flat cultures exist in a high energy state (oxidative phosphorylation), are glycolytic, and depend on glucose and glutamine for growth. In contrast, cells in organotypic culture exhibit lower energy and glycolysis, with extensive metabolic plasticity to maintain growth during glucose or amino acid deprivation. Expression of KRASG12V in organotypic cells drives glucose dependence, however cells retain metabolic plasticity to glutamine deprivation. Finally, our data reveal that mechanical properties control metabolic plasticity, which correlates with canonical Wnt signaling. In summary, our work highlights that the architectural and mechanical properties influence cells to permit or restrict metabolic plasticity.

Numb regulates cell tension required for mammary duct elongation.

The mammary gland undergoes extensive expansion of a ductal network through the stroma during puberty and is an excellent model for understanding epithelial tube morphogenesis. To investigate a role for Numb, a multifaceted adapter protein, in epithelial tube morphogenesis, we conditionally deleted it from the mammary epithelium. We report that Numb-depletion results in altered extracellular-matrix organization, reduced cell tension, altered cell shape, and increased cell packing density, which results in a 50% reduction in mammary duct elongation. Using laser ablation in vitro and geometric-based cell force inference in vivo, we determined that Numb-deficient cells have altered cortical tension. Duct elongation defects were associated with altered E-cadherin distribution, but were independent of proliferation, apoptosis in ducts or end buds. This highlights a critical role for Numb in a mechanical mechanism that is required to maintain cell packing density during epithelial tube elongation.

Progressive polarity loss and luminal collapse disrupt tissue organization in carcinoma.

Epithelial cancers (carcinoma) account for 80%-90% of all cancers. The development of carcinoma is associated with disrupted epithelial organization and solid ductal structures. The mechanisms underlying the morphological development of carcinoma are poorly understood, but it is thought that loss of cell polarity is an early event. Here we report the characterization of the development of human breast lesions leading to carcinoma. We identified a unique mechanism that generates solid ducts in carcinoma through progressive loss of polarity and collapse of the luminal architecture. This program initiates with asymmetric divisions of polarized cells that generate a stratified epithelium containing both polarized and depolarized cells. Stratified regions form cords that penetrate into the lumen, subdividing it into polarized secondary lumina. The secondary lumina then collapse with a concomitant decrease in RhoA and myosin II activity at the apical membrane and ultimately lose apical-basal polarity. By restoring RhoA activity in mice, ducts maintained lumen and cell polarity. Notably, disrupted tissue architecture through luminal collapse was reversible, and ducts with a lumen were re-established after oncogene suppression in vivo. This reveals a novel and common mechanism that contributes to carcinoma development by progressively disrupting cell and tissue organization.

Emerging role of cell polarity proteins in breast cancer progression and metastasis.

Breast cancer is a heterogeneous group of diseases that frequently exhibits loss of growth control, and disrupted tissue organization and differentiation. Several recent studies indicate that apical-basal polarity provides a tumor-suppressive function, and that disrupting polarity proteins affects many stages of breast cancer progression from initiation through metastasis. In this review we highlight some of the recent advances in our understanding of the molecular mechanisms by which loss of apical-basal polarity deregulates apoptosis, proliferation, and promotes invasion and metastasis in breast cancer.

Sensitization of human melanoma cells by tamoxifen to apoptosis induction by pancratistatin, a nongenotoxic natural compound.

The objective of this study was to determine the efficacy of the natural compound pancratistatin (PST), isolated from the Hymenocallis littoralis, in human melanoma cells. Melanoma is an aggressive form of skin cancer that is commonly fatal if not diagnosed in its early stage of development. Melanoma is resistant to many treatments, thus drastically limiting chemotherapy options for this cancer. We have shown that exposure to PST induces apoptosis in human melanoma within 72 h using Hoechst staining. Interestingly tamoxifen (TAM), an estrogen receptor antagonist, sensitizes these cells to apoptosis induction by PST as observed with Hoechst and annexin-V staining. This cotreatment did not affect the viability of normal noncancerous human fibroblasts. Both of these compounds have been shown to target the mitochondria synergistically, as indicated by higher levels of reactive oxygen species generation from isolated mitochondria. PST alone and in combination with TAM shows depolarization of the mitochondrial membrane potential as shown by JC-1 staining. Melanoma drug resistance was not observed after posttreatment recuperation, as cells displayed apoptotic morphology up to 96 h after drug-free media replacement. Our results indicate that TAM alone does not induce apoptosis in this cell line, but sensitizes the mitochondria, thereby enhancing the effect of PST exposure. In conclusion, combination of two nongenotoxic compounds offers a novel treatment regime for this notoriously resilient form of skin cancer.

Chemo-resistant melanoma sensitized by tamoxifen to low dose curcumin treatment through induction of apoptosis and autophagy.

Melanoma is the deadliest form of skin cancer, which is notoriously aggressive and chemo-resistant, and for which there is little effective treatment available if it goes undetected. Curcumin from the turmeric spice (Curcuma longa) has long been used in Southeast Asian medicine to alleviate ailments and cure an array of diseases and disorders. It possesses anti-inflammatory, anti-oxidant and most importantly anti-carcinogenic activity. There have been contradictory reports discussing the efficacy of curcumin-induced death on melanoma. In this report we show that curcumin does induce apoptosis in A375 and the relatively resistant G361 malignant human melanoma cell lines at higher doses. Tamoxifen is an estrogen receptor (ER) blocker that is used for ER positive breast cancer treatment. Recently, tamoxifen has been shown to directly target the mitochondria. Given that curcumin is a pro oxidant and tamoxifen can act on mitochondria, we ask whether the combinatorial treatment could result in synergistic induction of apoptosis in chemo-resistant melanoma. Our results show a corresponding increase in phosphatidyl serine flipping, mitochondria depolarization and reactive oxygen species (ROS) generation by the combined treatment at lower doses. Interestingly, there was significant induction of autophagy along with apoptosis following the combined treatment. Importantly, non-cancerous cells are unaffected by the combination of these non-toxic compounds. However, once exposed to low doses of this co-treatment, melanoma cells still retain signals to commit suicide even after removal of the drugs. This combination provides a non-toxic option for combinatorial chemotherapy with great potential for future use.