Dynamic altruistic cooperation within breast tumors

BACKGROUND

Social behaviors such as altruism, where one self-sacrifices for collective benefits, critically influence an organism's survival and responses to the environment. Such behaviors are widely exemplified in nature but have been underexplored in cancer cells which are conventionally seen as selfish competitive players. This multidisciplinary study explores altruism and its mechanism in breast cancer cells and its contribution to chemoresistance.

METHODS

MicroRNA profiling was performed on circulating tumor cells collected from the blood of treated breast cancer patients. Cancer cell lines ectopically expressing candidate miRNA were used in co-culture experiments and treated with docetaxel. Ecological parameters like relative survival and relative fitness were assessed using flow cytometry. Functional studies and characterization performed in vitro and in vivo include proliferation, iTRAQ-mass spectrometry, RNA sequencing, inhibition by small molecules and antibodies, siRNA knockdown, CRISPR/dCas9 inhibition and fluorescence imaging of promoter reporter-expressing cells. Mathematical modeling based on evolutionary game theory was performed to simulate spatial organization of cancer cells.

RESULTS

Opposing cancer processes underlie altruism: an oncogenic process involving secretion of IGFBP2 and CCL28 by the altruists to induce survival benefits in neighboring cells under taxane exposure, and a self-sacrificial tumor suppressive process impeding proliferation of altruists via cell cycle arrest. Both processes are regulated concurrently in the altruists by miR-125b, via differential NF-κB signaling specifically through IKKβ. Altruistic cells persist in the tumor despite their self-sacrifice, as they can regenerate epigenetically from non-altruists via a KLF2/PCAF-mediated mechanism. The altruists maintain a sparse spatial organization by inhibiting surrounding cells from adopting the altruistic fate via a lateral inhibition mechanism involving a GAB1-PI3K-AKT-miR-125b signaling circuit.

CONCLUSIONS

Our data reveal molecular mechanisms underlying manifestation, persistence and spatial spread of cancer cell altruism. A minor population behave altruistically at a cost to itself producing a collective benefit for the tumor, suggesting tumors to be dynamic social systems governed by the same rules of cooperation in social organisms. Understanding cancer cell altruism may lead to more holistic models of tumor evolution and drug response, as well as therapeutic paradigms that account for social interactions. Cancer cells constitute tractable experimental models for fields beyond oncology, like evolutionary ecology and game theory.

Propagation of nonparaxial beams with a modified Arnoldi method

We have developed a modified Arnoldi method that includes a complex square-root approximation, which excels at modeling the propagation of highly diverging beams in various media. Simulations of one transverse dimensional beam with an ultranarrow width and of cylindrical Gaussian beams with various divergence angles reveal the strength of this nonparaxial-beam propagation method.

Nonparaxial propagation of a cylindrical beam with Lanczos reduction

We discuss a numerical method based on Lanczos reduction of modeling nonparaxial propagation of a cylindrical symmetric beam. To illustrate the performance and demonstrate the significant difference between nonparaxial and paraxial beams, we consider Gaussian beam propagation in two different settings.

Waveguiding properties of optical vortex solitons

An optical vortex soliton induces a graded-index waveguide over an extended propagation distance in a self-defocusing nonlinear optical medium. Using numerical techniques, we determine the waveguide dispersion and optimal size of the guided beam.

Strong excitonic nonlinearity in a P-I-N photodiode incorporating narrow asymmetric coupled quantum wells

Strong excitonic nonlinearity in the photoconductive response of a P-I-N photodiode incorporating narrow asymmetric coupled quantum wells has been observed at 78 K. When the P-I-N photodiode is overbiased, the heavyhole energy levels in the two coupled quantum wells are moved toward the resonance by increasing the laser intensity. Also, both the light-hole and the heavy-hole excitonic transitions undergo intensity-dependent shifts. Both these effects indicate intrinsic change of bias due to redistribution of photogenerated carriers and, therefore, the existence of an intrinsic feedback mechanism. The magnitude of the blue shift of the heavy-hole excitonic transitions significantly increases when the laser intensity is changed from 9.2 to ~270 mW/cm(2).

Dispersion-related amplification in a nonlinear fiber pumped by counterpropagating waves

We investigate the dispersion-related amplification induced by two counterpropagating waves in a nonlinear fiber and demonstrate that this system can provide broadband (of the order of terahertz) and large (>10(5)) amplification even in the presence of absorption, with the pumping significantly below the threshold of instability.

Dispersion-related multimode instabilities and self-sustained oscillations in nonlinear counterpropagating waves

We show that two linearly polarized counterpropagating waves in a Kerr nonlinear medium with linear dispersion can exhibit multimode temporal instability. We find the boundary of the unstable regime and demonstrate that the fully developed instability results in self-sustained oscillations and the onset of chaos.

X-ray transition radiation in a solid-state superlattice: photoabsorption, electron scattering, and radiation optimization

Soft x rays are generated when low-energy electron beams traverse a solid-state superlattice. We investigate the influence of x-ray absorption and electron scattering losses on the maximum power radiated, the required electron energy, and the optimum total thickness of the superlattice. We show that a moderate increase in the electron-beam energy compensates for the losses due to photoabsorption and electron scattering.