Gets activated within the occasion of AMAS Biological Activity topoisomerase inhibition or chemical induced DNA harm [26]. Double staining of Topo II and DNA-PK in cryptolepine treated or untreated NMSC cells revealed that it inhibits topoisomerase expression when enhances DNA repair enzyme DNA-PK. DNA harm response pathway involves damage sensors, signal transducers, and effectors [36,37]. DNA damage triggers activation of DNA damage response components, for instance ATM and ATR. Activation of ATR is normally related with damage to single-strand DNA or stalled DNA replication forks even though activation of ATM is linked with initiation of signaling pathways in response to double strand breaks [37,38]. We’ve identified that treatment of NMSC cells with cryptolepine induces phosphorylation of both ATM and ATR proteins in SCC-13 and A431 cells. Through inhibition of topoisomerase activity, activated ATM and ATR straight or by means of sequential measures phosphorylate downstream proteins BRCA1, H2AX, Chk1 and Chk2 and subsequently impact downstream variables involved in cell cycle progression and cell survival [18,21,22]. Phosphorylated H2AX and BRCA1 are involved in DNA repair and activation of other repair elements, whereas, phosphorylated Chk1 and Chk2 activate factors involved in cell cycle arrest and apoptosis [30]. As a consequence of cryptolepine induced DNA damage in SCC-13 and A431 cells, BRCA1, H2AX, Chk1 and Chk2 have been tremendously phosphorylated. Phosphorylation of BRCA1, H2AX, Chk1 and Chk2 observed in cryptolepine treated cells is also supported by the evidences thatMolecules 2016, 21,11 ofhave demonstrated that clinically employed cancer chemotherapeutic agents which inhibit topoisomerase functions also activate these signaling cascade [20,23]. The tumor suppressor protein p53 can be a vital component of cellular machinery that regulates many signaling pathways such as oncogenic processes, cell cycle, apoptosis and DNA damage responses beneath diverse circumstances. Beneath typical circumstances, in unstressed cells, the expression and function of p53 are tightly regulated and maintained in low levels with quick half-life [28,39]. Having said that, below stressed circumstances, like induction of DNA damage, nucleotide depletion, or hypoxia, levels of p53 protein increases substantially. The mechanism of enhanced p53 levels after DNA damage is believed to become post-translational modifications like phosphorylation and acetylation [28,40,41]. In response to topoisomerase inhibition or chemically induced DNA harm, activated ATM or Chk2 directly activates p53 by phosphorylation or inhibits its interactions with unfavorable regulator mdm2. Mdm2 protein attenuates p53 activity either by way of auto-regulatory loop by interacting with amino terminus of p53 or by activating degradation method. CDK inhibitory proteins p21 and p16 are key downstream proteins transcriptionally activated by p53. Enhanced expression of p21 and p16 proteins inhibits cell cycle progression and induces apoptosis [36,42]. Outcomes from our experiments clearly demonstrates that cryptolepine induced topoisomerase inhibition and induction of DNA harm in SCC-13 and A431 cells resulted in activation and accumulation of p53 protein through enhanced phosphorylation and acetylation. Cryptolepine treatment also down regulates the degree of mdm2 protein in these cells. Moreover, expression of p16 and p21 was also enhanced because of activation of p53 in these cells after cryptolepine induced DNA damage. Moreover, activated p53 and p16 and p2.