Fig.: to do something harmful, to betray or sacrifice a person, who trusts you and is working with or for you, in order to get a personal advantage or safeguard your own interests

Here's the thing: the director was in very strong contrast with the aspiring star of his film, so much so that, at the first opportunity, he threw him under the bus on live TV

Le cose stanno così: il regista era in fortissimo contrasto con l'aspirante protagonista del suo film, tanto che alla prima occasione lo ha scaricato in diretta TV

He's been accused of throwing his fellows republicans under the bus for his personal agenda

È stato accusato di avere scaricato i suoi colleghi repubblicani per fare il proprio interesse

Don't ever trust him! I know him well and I know that if he needs you, he likes you. If you are of no use to him anymore, he doesn't care and he will throw you under the bus

Non fidarti mai di lui! Lo conosco bene e so che se ha bisogno di te, gli piaci; ma quando non gli servi più, ti scarica all'istante senza nessun problema