The phosphatidylinositol 3-kinase (PI3K)/Akt pathway elicits a survival signal against multiple apoptotic insults. In addition, phase II enzymes such as heme oxygenase-1 (HO-1) protect cells against diverse toxins and oxidative stress. In this work, we describe a link between these defense systems at the level of transcriptional regulation of the antioxidant enzyme HO-1. The herb-derived phenol carnosol induced HO-1 expression at both mRNA and protein levels. Luciferase reporter assays indicated that carnosol targeted the mouse ho1 promoter at two enhancer regions comprising the antioxidant response elements (AREs). Moreover, carnosol increased the nuclear levels of Nrf2, a transcription factor governing AREs. Electrophoretic mobility shift assays and luciferase reporter assays with a dominantnegative Nrf2 mutant indicated that carnosol increased the binding of Nrf2 to ARE and induced Nrf2-dependent activation of the ho1 promoter. While investigating the signaling pathways responsible for HO-1 induction, we observed that carnosol activated the ERK, p38, and JNK pathways as well as the survival pathway driven by PI3K. Inhibition of PI3K reduced the increase in Nrf2 protein levels and activation of the ho1 promoter. Expression of active PI3K-CAAX (where A is aliphatic amino acid) was sufficient to activate AREs. The use of dominant-negative mutants of protein kinase C and Akt1, two kinases downstream from PI3K, demonstrated a requirement for active Akt1, but not protein kinase C. Moreover, the long-term antioxidant effect of carnosol was partially blocked by PI3K or HO-1 inhibitors, further demonstrating that carnosol attenuates oxidative stress through a pathway that involves PI3K and HO-1.High levels of reactive oxygen species cause damage to cells and are involved in several human pathologies, including neurodegenerative disorders and cancer (1, 2). Therefore, the use of compounds with antioxidant properties may help prevent or alleviate diseases in which oxidative stress is a primary cause (3). Carnosol, a diterpene derived from the herb rosemary, is a representative member of a family of plant-derived phenols, which also include curcumin, carnosic acid, phenylethyl isothiocyanate, epigallocatechin gallate, and other green tea polyphenols. These bioactive phytochemicals exhibit Michael acceptor function and therefore behave as antioxidants (4). In addition, being themselves xenobiotic compounds, they activate a xenobiotic response in the target cells affecting the expression of phase II enzymes such as NAD(P)H:quinone oxidoreductase, aldoketoreductase, glutathione S-transferase, ␥-glutamylcysteine synthetase, glutathione synthetase, and heme oxygenase-1 (HO-1) 1 (5-7). Heme oxygenase isozymes (HO-1 and HO-2) catalyze the stepwise degradation of heme to release free iron and equimolar concentrations of carbon monoxide and the linear tetrapyrrole biliverdin, which is converted to bilirubin by the enzyme biliverdin reductase (8). The HO-1 isozyme is a phase II enzyme that is transcriptionally regulated by a large...