Project 467070

Two major pathways cells use to repair DNA double-strand breaks (DSB) are homologous recombination (HR) and non-homologous end joining (NHEJ). BRCA1 steers cells toward HR and mutations in BRCA1 increase the likelihood of breast cancer. Additionally, a common feature of cancer cells is an abundance of invaginations of the nuclear envelope (NE). Preliminary data from our laboratory suggest that NE invaginations play a role in DSB repair. Upon the induction of DSB, a network of NE invaginations called nano nuclear envelope tubules (nanoNET) localize to sites rich in NHEJ proteins. nanoNET is driven by the kinesin KIF5B and limited by KIFC3, both of which travel along microtubules in opposite directions. Interestingly, breast cancers demonstrate highly invaginated nuclei, upregulation of KIF5B, downregulation of KIFC3, and BRCA1-deficient breast cancer cells are reliant on NHEJ. Therefore, we hypothesize that BRCA1-deficient cells benefit from DSB repair by nanoNET that is promoted by KIF5B and limited by KIFC3, which can be exploited to restrain BRCA1-deficient cell survival and tumor growth. We will use BRCA1-deficient human breast cancer models with KIF5B and KIFC3 knockdown (KD) in both in vitro and in vivo systems to determine if (1) the inhibition of nanoNET limits faithful DSB repair in BRCA1-deficient cells and (2) the promotion of nanoNET can enhance the synthetic lethality of PARP inhibitors and BRCA1-deficiency. 3D microscopy techniques will be used to capture the effect of the KIF KD on nanoNET formation. This work has the potential to not only elucidate a functional role of NE invaginations in genome stability but can also reveal avenues to maximize the therapeutic efficacy of chemotherapeutic drugs to better target BRCA1-deficient breast cancers.