Cells transduce mechanical forces into biochemical signals; traditionally these processes are thought to occur through direct effects on the cell membrane, the cytoskeleton, or specific transmembrane proteins. In multicellular tissues mechanical forces alter intercellular spacing through redistribution of interstitial fluid. Recent morphological and biochemical observations, bolstered by analytical modeling, support a new paradigm for mechanotransduction arising from constitutive growth factor shedding into a dynamically regulated interstitial volume.

14350-14355, 2005). In the work described here, we show that the E295K gastric carcinoma pol ␤ variant acts in a dominant-negative manner by interfering with base excision repair. This leads to an increase in sister chromatid exchanges. Expression of the E295K variant also induces cellular transformation. Our data suggest that unfilled gaps are channeled into a homology-directed repair pathway that could lead to genomic instability. The results indicate that base excision repair is critical for maintaining genome stability and could therefore be a tumor suppressor mechanism.

Thirty percent of the 189 tumors studied to date express DNA polymerase ␤ variants. One of these variants was identified in a prostate carcinoma and is altered from isoleucine to methionine at position 260, within the hydrophobic hinge region of the protein.Another variant was identified in a colon carcinoma and is altered at position 289 from lysine to methionine, within helix N of the protein. We have shown that the types of mutations induced by these cancer-associated variants are different from those induced by the wild-type enzyme. In this study, we show that expression of the I260M and K289M cancer-associated variants in mouse C127 cells results in a transformed phenotype in the great majority of cell clones tested, as assessed by focus formation and anchorageindependent growth. Strikingly, cellular transformation occurs after a variable number of passages in culture but, once established, does not require continuous expression of the polymerase ␤ variant proteins, implying that it has a mutational basis. Because DNA polymerase ␤ functions in base excision repair, our results suggest that mutations that arise during this process can lead to the onset or progression of cancer.base excision repair ͉ DNA repair ͉ mutagenesis S pontaneous DNA damage occurs at a rate of Ϸ10,000 lesions per cell per day, and much of this damage is repaired by the base excision repair (BER) machinery (1, 2). The BER system plays a critical role in maintaining cellular genomic stability. During BER, damaged bases are removed by a DNA glycosylase, followed by incision of the DNA by AP endonuclease (APE) at a position that is usually 5Ј to the lesion, leaving a nick with a 3ЈOH and a 5Ј deoxyribose phosphate (2). DNA polymerase beta (pol ␤) binds to the nick, removes the deoxyribose phosphate with its DRP lyase activity (3), and fills in the single nucleotide gap, using its DNA polymerase activity (4).Fifty-eight of the 189 tumors characterized to date express DNA pol ␤ variant proteins (for review, see ref. 5) (6). Of these, 28 (48%) expressed variants with single amino acid alterations, seven expressed truncated forms of pol ␤, and eight expressed multiple variant forms of pol ␤. These mutations are absent from normal tissue from the same individuals and are not among the common polymorphisms found within the pol ␤ gene (http:͞͞ egp.gs.washington.edu͞data͞polb) (5, 7). In addition, an alternative splice variant of pol ␤ in which exon 11 is deleted was expressed in 15 tumors. This splice variant appears to interfere with BER (8). This exon 11 splice variant has been detected in normal tissue, including normal tissue isolated from 2 of 15 patients with tumors, and its link to cancer etiology remains controversial (9-12). Each of the tumors characterized to date also contain the wild-type (WT) pol ␤ allele.The I260M variant of pol ␤ was identified in a prostate carcinoma (13). Isoleucine 260 is located within a hydrophobic hinge region that appears to function in the movement of the fingers subdomain upon interaction of the polymeras...

Systemic lupus erythematosus (SLE) is distinct among autoimmune diseases due to its association with circulating autoantibodies reactive against host DNA. The precise role that anti-DNA antibodies play in SLE pathophysiology remains to be elucidated, and potential applications of lupus autoantibodies in cancer therapy have not previously been explored. Here we report the unexpected finding that a cell-penetrating lupus autoantibody, 3E10, has potential as a targeted therapy for DNA-repair deficient malignancies. We find that 3E10 preferentially binds DNA single-strand tails, inhibits key steps in DNA single-strand and double-strand break repair, and sensitizes cultured tumor cells and human tumor xenografts to DNA-damaging therapy, including doxorubicin and radiation. Moreover, we demonstrate that 3E10 alone is synthetically lethal to BRCA2-deficient human cancer cells and selectively sensitizes such cells to low dose doxorubicin. Our results establish an approach to cancer therapy that we expect will be particularly applicable to BRCA2-related malignancies such as breast, ovarian, and prostate cancers. In addition, our findings raise the possibility that lupus autoantibodies may be partly responsible for the intrinsic deficiencies in DNA repair and the unexpectedly low rates of breast, ovarian, and prostate cancers observed in SLE patients. In summary, this study provides the basis for the potential use of a lupus anti-DNA antibody in cancer therapy and identifies lupus autoantibodies as a potentially rich source of therapeutic agents.

Studies show that 30% of 189 tumors sequenced to date express variants of the polymerase beta (pol beta) protein that are not present in normal tissue. This raises the possibility that variants of pol beta might be linked to the etiology of cancer. Here, we characterize the I260M prostate-cancer-associated variant of pol beta. Ile260 is a key residue of the hydrophobic hinge that is important for the closing of the polymerase. In this study, we demonstrate that the I260M variant is a sequence context-dependent mutator polymerase. Specifically, I260M is a mutator for misalignment-mediated errors in dipyrimidine sequences. I260M is also a low-fidelity polymerase with regard to the induction of transversions within specific sequence contexts. Our results suggest that the hinge influences the geometry of the DNA within the polymerase active site that is important for accurate DNA synthesis. Importantly, characterization of the I260M variant shows that it has a functional phenotype that could be linked to the etiology or malignant progression of human cancer.