The Structure of the Cell Nucleus and Cancer Chemoresistance

Farzaneh Atrian Afyani, Purdue University

Abstract

Cancers have the ability to develop resistance to traditional therapies. The important role of the tumor microenvironment in transforming nonaggressive tumor cells into an aggressive and chemoresistant cancer has been abundantly addressed. Mechanical cues from the tumor environment, such as matrix stiffness and geometry, transfer to the cell nucleus via the cytoskeleton and change nuclear morphology (e. g, chromatin organization, size and shape). Such alterations are known to accompany or follow the acquisition of chemoresistance. Nuclear matrix proteins such as the Nuclear Mitotic Apparatus (NuMA) are highly involved in higher order chromatin organization and contribute to sustain the physical structure of the cell nucleus, but it is yet to be determined how such structural proteins respond to microenvironmental changes. We have shown previously that tumors cultured in curved geometry (similar to the ductal architecture of breast tissue) display significantly different drug sensitivities compared to those cultured on a flat surface, and that a major morphological difference between these two culture conditions is nuclear shape (i.e., circularity). Our hypothesis is that mechanical cues from the tumor microenvironment alter nuclear features that control the phenotypic response of cancer cells to antiproliferative drugs. Morphological analysis of the cell nucleus in the curved conformation as well as hydrogel and hanging drop systems (with amorphous geometry) showed that only nodules in the curved set-up have nuclear morphometry (shape and size) similar to that of breast tumors of the corresponding subtypes in vivo. In addition, we compared the sensitivity of triple negative breast tumors to cisplatin, with proven efficacy in the clinics, and SAHA, an epigenetic drug that so far failed in breast cancer treatment. Our results suggest higher sensitivity to cisplatin and lower sensitivity to SAHA of breast cancer cells cultured in duct-like geometry compared to the amorphous systems. To evaluate the importance of nuclear morphometry in drug response we altered nuclear size and shape using latrunculin. Under this condition, the number of apoptotic and growth-arrested cells increased following treatments with cisplatin and SAHA, respectively.Nuclear morphometry was also modified by spreading cells over fibronectin-coated micropatterned surfaces. Cisplatin treatment revealed higher sensitivity of cells with bigger compared to smaller nuclear area. The nuclei with increased area had the highest number of 53BP1 foci, representing DNA double strand breaks, hence confirming a positive link between nuclear morphometry and drug sensitivity. Silencing NuMA in conventional monolayered cell cultures significantly increased nuclear size, redistributed 53BP1 within the nucleus and was linked with increased sensitivity to cisplatin and SAHA. To validate the relationship between drug sensitivity, nuclear morphometry and NuMA, in a physiologically relevant manner we cultured chemoresistant and chemosensitive breast tumors that were nonsilenced/silenced for NuMA in collagen matrix with adjustable stiffness. Nuclear morphometric analysis indicated that nuclear size and shape are unique characteristics of tumors with different phenotypes, and the impact of nuclear morphometry on drug response depended on the tumor phenotype and matrix stiffness. Moreover, high matrix stiffness reduced drug sensitivity independently of the tumor phenotype, and the influence of NuMA on nuclear size and shape and on drug sensitivity occurred in a stiffness-dependent manner. For example, low NuMA expression in high matrix rigidity was significantly associated with higher cisplatin sensitivity only in chemoresistant cells. Overall, regression analysis demonstrated that, the low NuMA expression is the major determinant of drug sensitivity in cells with different levels of chemosensitivity.

Degree

Ph.D.

Advisors

Lelièvre, Purdue University.

Subject Area

Physiology|Biochemistry|Cellular biology|Genetics|Medicine|Oncology|Pharmaceutical sciences|Pharmacology|Therapy

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